Just received a copy of the UK journal Mathematical Spectrum, vol. 40, no. 1 (2007/2008), which includes an article on the Picture Perfect Numbers (pp. 17–23), on which research I worked a few years ago with the author Joseph Pe, along with Mark Ganson and Jens Kruse Andersen.
Daniel Dockery's Portfolio
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Appearances: Barcelona
Today I had the chance to see the Barcelona edition of Dr. Pickover’s book The Mathematics of Oz, translated by Richard Ley. Page 363 was curiously amusing:
El amigo del Dr. Oz, Daniel Dockery, ha observado algo interesante acerca de los valores de x que producen números primos usando esta fórmula. En todos los casos realizó pruebas para los valores de x, 0 ≤ x ≤ 5000, la suma del os dígitos x igual a 2 + 3n. Esto también puede ser verdad para valores mayores de x. Por ejemplo, considere x = 999.999.999.764 (lo cual produce el primo 999.999.999.527.000.000.275.457 usando esta fórmula). Este valor de x tiene una suma de dígitos de 98, la cual es 2 + 3 × 32.
Las matemáticas de Oz: Gimnasia mental más allá del límiteBiblical numbers
Dr. Pickover asked, “What kinds of numbers did Jesus use (or someone of his era)?”
Since it’s claimed he spoke Aramaic, I expect he’d have used the Aramaic/Hebrew number system where their alphabetic characters also served as their numbers. (The languages, of course, also had names for the numbers, just as we have “1” and “one”, etc.; I’m just referring to how numbers were written.) Since some of the apocryphal and pseudepigraphic infancy gospels tell tales of his having discoursed on the symbolism of the Greek & related alphabets, one might also argue that he could have written using the Greek number system, which likewise used its alphabet for numerical digits. If you consider the text of the “New Testament” as definitive, all numbers that appear in passages with references to Jesus in the four gospels are written out in Greek (e.g., εἷς/μία/ἕν [one], δύο or δύω [two], τρεῖς/τρία [three], τέσσαρες/τέσσαρα [four], ἕξ [six], ἑπτά [seven], ὀκτώ [eight], ἑπτάκις [seven times], ἐννέα [nine], δέκα [ten], εἴκοσι πέντε [twenty five], τριάκοντα [thirty], ἑκατόν [one hundred], ἑβδομηκοντάκις ἑπτά [seventy times seven], δισχίλιοι [two thousand], πεντακισχίλιοι [five thousand], etc.) Most numbers in the text tend to be written out, though there are a few exceptions: e.g., the infamous “666” of the Apocalypse is written with the three Greek letters chi (χ), xi (ξ) and the antiquated stigma (Ϛ); in the Greek numeral system, the letter χ has a value of 600, ξ 60 and Ϛ/Ϝ a value of 6, so that the three letters appearing together as a number have the combined value of 666. (See also the article, “Arithmology in the Bible“).
Further, he asked, “Do you think he could multiply?”
It would be hard to say, but perhaps the text can be taken in support with passages such as:
λέγει αὐτῷ ὁ Ἰησοῦς· οὐ λέγω σοι ἕως ἑπτάκις ἀλλὰ ἕως ἑβδομηκοντάκις ἑπτά.
dicit illi Iesus non dico tibi usque septies sed usque septuagies septies
Said Jesus: To you I say not ’til seven times,’ but ‘until seventy times seven.’
Matthew 18:22
While both seven & seventy can have symbolic meanings, the passage may not be literal, but nevertheless it is an example of the idea of multiplication—though I don’t think it really makes it clear whether he or his listeners would have been able to give the answer.
Having also asked why 0 wouldn’t have been used: neither the Hebrew, Aramaic nor Greek number systems had a character representing the number 0, as it wasn’t needed by non-positional number systems. There’s a whole section on the emergence of zero in Ifrah’s The Universal History of Numbers: From Prehistory to the Invention of the Computer, if I recall correctly.
Obstinate Numbers
Dr. Pickover commented:
In 1848, Camille Armand Jules Marie, better known as the “Prince de Polignac,” conjectured that every odd number is the sum of a power of two and a prime. (For example 13 = 23+5.) He claimed to have proved this to be true for all numbers up to three million, but de Polignac probably would have kicked himself if he had know that he missed 127, which leaves residuals of 125, 123, 119, 111, 95 and 63 (all composites) when the possible powers of two are subtracted from it. There are another 16 of these odd numbers—which my colleague Andy Edwards calls “obstinate numbers”—that are less than 1000. There are an infinity of obstinate numbers greater than 1000. Most obstinate numbers we have discovered are prime themselves. The first composite obstinate number is 905.
Then he asked:
What is the largest obstinate number you can compute?
Can you find an obstinate number terminating in every digit from 0 to 9, or are certain terminal digits impossible to find?
Other unanswered questions:
1) What is the smallest difference between adjacent obstinates?
2) Do any obstinates undulate? (Undulating numbers are of the form: ababababab… For example, 171717 and 28282 are undulating numbers, but they’re not obstinate, as far as I know.)
If you make discoveries, give us some ideas about the kinds of search programs you used.
Curiosity piqued, I looked into the subject. As far as I can tell, the only upper limit as to the size of potentially “obstinate” numbers would be the amount of computer processing power you’d want to put into it. I ran an extensive search and there was no appreciable lessening to the frequency of the numbers and no suggestion that they would “level off” at any point, so I have no reason to not suppose they are an infinite set. The largest I have found so far is:
999999999999999999999999999999999999999999999999999999999999999 999999999999999999999999999999999999999999999999999999999999999 9999999999999999999999999999999999999999999999999999999999037
I stopped there not because I’d reached the limits of my processing power, but only because I’d reached the limit of my patience for waiting for further results. It leaves a composite residue for all 621 possible powers of two than can be subtracted from it. Later, this result increased to:
999999999999999999999999999999999999999999999999999999999999999 999999999999999999999999999999999999999999999999999999999999999 999999999999999999999999999999999999999999999999999999999999999 999999999999999999999999999999999999999999999999999999999999999 999999999999999999999999999999999999999999999999999999999999999 999999999999999999999999999999999999999999999999999999999999999 999999999999999999999999999999999999999999999999999999999999999 999999999999999999999999999999999999999999999999999999999999999 9999999011
This leaves 1,708 powers of two in the residue. (This number has since been increased; see the article, Obstinate Numbers in the Triangle of the Gods.)
Dr. Pickover also asked if obstinate numbers could terminate in all ten natural digits. I suspect he was trying to trip one up with that since the very definition of obstinate numbers requires them to be odd—as such, they cannot end with an even digit. All odd digits are accounted for, however, in the results I have so far found. As far as the question about the smallest difference between adjacent obstinates, it has to be two. Both 905 and 907 are obstinate, and since obstinate numbers must be odd, two is the smallest possible difference. I would be interested, myself, in the largest difference, and I will probably run a search for it later, but I haven’t yet. When I do, I’ll update these notes. He asked about undulation, and from what I can see, it doesn’t seem to be at all uncommon with these numbers. At a glance, these undulating numbers are all obstinate:
6161 14141 39393 91919 1313131 1818181 7070707 7474747 7676767 7979797 59595959 73737373 343434343 757575757 797979797 929292929 1717171717 3131313131 9191919191 12121212121 14141414141 18181818181 32323232323 54545454545 78787878787 91919191919 7171717171717 25252525252525 29292929292929 37373737373737 43434343434343 67676767676767 97979797979797
I’m certain there are others; I simply didn’t bother continuing the search at higher numbers.
As far as the question as to what search programs were used, for the above I simply wrote two Maple functions—one to check for obstinacy and another to print a list of composite residues. Once those two were in place, the search was easy—just a matter of waiting. For any interested parties, I’ll reproduce the body of the two functions here. They can probably be optimized, but I’m not an especially adept Maple coder (Maple code reminds me far too much of BASIC and that gives me nightmares).
with(numtheory):
isObstinate := proc(o)
local pp, p, a, z:
if o mod 2 <> 0 then
pp := 0: a := floor(log[2](o)):
for z to a do
p := o - 2^z:
if isprime(p) then pp := 1 fi:
od:
if pp = 0 then true else false fi:
else
printf("Must be oddn"):
fi:
end:
showResidue := proc(n)
local a, z, p:
a := floor(log[2](n)):
for z to a do
p := n - 2^z:
if not isprime(p) then
printf("2^%d + %dn",z,p)
fi:
od:
end:With those it’s simply a matter of running through the odd numbers and checking isObstinate(number). If a residue list is desired, just throw an obstinate number to showResidue(number). (Note that the latter function assumes you’re feeding it an obstinate number: it doesn’t check to see if you have, or if all of the residue values printed are composite. With the way I used it, there was no point in having the redundant code so I omitted it.)
Slightly more structured test conditions for Mathematica:
ObstinateQ[n_Integer /; n > 0] :=
If[OddQ[n],
If[Intersection[
Table[PrimeQ[n - 2^j], {j, 1, Floor[Log[2, n]]}],
{True}] == {},
True, False
],
Print["Must be odd."]
]
NPResidue[n_Integer /; ObstinateQ[n]] :=
If[
rt = Table[n - 2^j, {j, 1, Floor[Log[2, n]]}];
Intersection[Map[PrimeQ, rt], {True}] == {},
rt,
Print["Residue includes Prime(s)."]
]
A last note, Dr. Pickover remarked that “most” obstinate numbers they’d found were prime numbers themselves. It leads me to believe that they didn’t research much beyond the 1000 point since from the lowest obstinate number, 127, to 100,000, I found a total of 3,392 obstinate numbers, 2,147 of which were composite: the 1,245 prime values were clearly the minority. Considering the decreasing frequency of primes in general as numbers grow increasingly larger, and the seeming continued regularity of obstinate numbers, it seems that the nonprime values will naturally continue to widen the gap between themselves and their prime counterparts.
Triangle of the Gods
Dr. Pickover proposes the problem,
An angel descends to Earth and shows the following simple progression of numbers:
1
12
123
1234
12345
123456
1234567
12345678
… etc.The angel will let you enter the afterlife if you can address two or more of the questions below in a satisfactory manner:
What is the first and second prime number we encounter on this triangle?
2) What percentage of prime numbers do you expect as we scan more rows in the mysterious triangle?
If you could add one digit to the beginning of each number in order to increase the number of primes, what would it be? Justify your answer.
If you could add one digit to the end of each number in order to increase the number of primes, what would it be? Justify your answer.
What is the largest prime number in this progression known to humanity?
Given the small sample size of the beginning of the triangle, I was uncertain which of two possible forms to pursue. For instance, is it generated by continuing to add the natrual numbers in sequence—would this continue 123456789, 12345678910, 1234567891011, etc.—or do the lines simply cycle through the single digits so that the next few lines would continue 123456789, 1234567890, 12345678901, 123456789012, etc.? Unsure, I replied to both cases; for convenience, I’ll refer to the first as the “natural” sequence, and the second as the “digit” sequence.
In the natural sequence, I found no prime numbers in the first five hundred thousand rows, yet in the digit sequence, I observed these:
Row 171:
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901
Row 277:
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567
Row 367:
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
1234567
Row 561:
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901
Row 567:
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567
I found no others in the first 1000 rows of the digit sequence.
For the third question, searching the first two hundred rows of the natural sequence, all digits 1 through 9 except for 5, 6 and 9 produced two primes when prefixed to the rows of the sequence. Six and nine produced one each, and I found none for 5 in this range. For reference, here are the rows and numbers which were prime for the given digits:
Prefixing 1:
Row 1:
11
Row 3:
1123
Prefixing 2:
Row 21:
2123456789101112131415161718192021
Row 69:
212345678910111213141516171819202122232425262728293031323334
353637383940414243444546474849505152535455565758596061626364
6566676869
Prefixing 3:
Row 1:
31
Row 19:
312345678910111213141516171819
Prefixing 4:
Row 1:
41
Row 17:
41234567891011121314151617
Prefixing 6:
Row 1:
61
Prefixing 7:
Row 1:
71
Row 7:
71234567
Row 183:
712345678910111213141516171819202122232425262728293031323334
353637383940414243444546474849505152535455565758596061626364
656667686970717273747576777879808182838485868788899091929394
959697989910010110210310410510610710810911011111211311411511
611711811912012112212312412512612712812913013113213313413513
613713813914014114214314414514614714814915015115215315415515
615715815916016116216316416516616716816917017117217317417517
6177178179180181182183
Prefixing 8:
Row 3:
8123
Row 39:
812345678910111213141516171819202122232425262728293031323334
3536373839
Prefixing 9:
Row 13:
912345678910111213
For the first two hundred rows of the digital sequence, prefixing 4 produced the most with 4 primes; 1, 6 and 7 each produced three primes; 3 and 5 each produced two; and 8 and 9 produced one each.
Prefixing 1:
Row 1:
11
Row 3:
1123
Row 161:
112345678901234567890123456789012345678901234567890123456789
012345678901234567890123456789012345678901234567890123456789
012345678901234567890123456789012345678901
Prefixing 3:
Row 1:
31
Row 11:
312345678901
Prefixing 4:
Row 1:
41
Row 17:
412345678901234567
Row 31:
41234567890123456789012345678901
Row 99:
412345678901234567890123456789012345678901234567890123456789
0123456789012345678901234567890123456789
Prefixing 5:
Row 49:
51234567890123456789012345678901234567890123456789
Row 59:
512345678901234567890123456789012345678901234567890123456789
Prefixing 6:
Row 1:
61
Row 41:
612345678901234567890123456789012345678901
Row 71:
612345678901234567890123456789012345678901234567890123456789
012345678901
Prefixing 7:
Row 1:
71
Row 7:
71234567
Row 19:
71234567890123456789
Prefixing 8:
Row 3:
8123
Prefixing 9:
Row 21:
9123456789012345678901
For the fourth question, from the first two hundred rows of the natural sequence, it would seem that attaching a 1 or a 7 would generate the most: adding 1 as a suffix produces 7 primes, adding 7 produces 8; adding 3 or 9 both produced three each.
1:
Row 1:
11
Row 3:
1231
Row 9:
1234567891
Row 11:
12345678910111
Row 16:
123456789101112131415161
Row 26:
12345678910111213141516171819202122232425261
Row 114:
123456789101112131415161718192021222324252627282930313233343
536373839404142434445464748495051525354555657585960616263646
566676869707172737475767778798081828384858687888990919293949
5969798991001011021031041051061071081091101111121131141
3:
Row 1:
13
Row 4:
12343
Row 97:
123456789101112131415161718192021222324252627282930313233343
536373839404142434445464748495051525354555657585960616263646
566676869707172737475767778798081828384858687888990919293949
596973
7:
Row 1:
17
Row 2:
127
Row 3:
1237
Row 4:
12347
Row 5:
123457
Row 21:
1234567891011121314151617181920217
Row 28:
123456789101112131415161718192021222324252627287
Row 107:
123456789101112131415161718192021222324252627282930313233343
536373839404142434445464748495051525354555657585960616263646
566676869707172737475767778798081828384858687888990919293949
5969798991001011021031041051061077
9:
Row 1:
19
Row 16:
123456789101112131415169
Row 22:
123456789101112131415161718192021229
I found it curious that the first five rows all became prime when attaching the digit 7.
For the digit sequence, the number of primes remains rather close to the same: 1 now produces eight primes, one more than in the natural sequence, and 9 now produces only two, one less than in the natural sequence; 3 and 7 still produce the same number of primes as in the natural sequence (3 and 8 respectively).
1:
Row 1:
11
Row 3:
1231
Row 9:
1234567891
Row 11:
123456789011
Row 17:
123456789012345671
Row 19:
12345678901234567891
Row 33:
1234567890123456789012345678901231
Row 170:
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901
3:
Row 1:
13
Row 4:
12343
Row 104:
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012343
7:
Row 1:
17
Row 2:
127
Row 3:
1237
Row 4:
12347
Row 5:
123457
Row 41:
123456789012345678901234567890123456789017
Row 54:
1234567890123456789012345678901234567890123456789012347
Row 91:
123456789012345678901234567890123456789012345678901234567890
12345678901234567890123456789017
9:
Row 1:
19
Row 54:
1234567890123456789012345678901234567890123456789012349
For the final question, of the largest prime number known: with regard to the natural sequence, I’m not certain, but it would have to be greater than
123456789101112131415161718192021222324252627282930313233343
536373839404142434445464748495051525354555657585960616263646
566676869707172737475767778798081828384858687888990919293949
596979899100101102103104105106107108109110111112113114115116
117118119120121122123124125126127128129130131132133134135136
137138139140141142143144145146147148149150151152153154155156
157158159160161162163164165166167168169170171172173174175176
177178179180181182183184185186187188189190191192193194195196
197198199200201202203204205206207208209210211212213214215216
217218219220221222223224225226227228229230231232233234235236
237238239240241242243244245246247248249250251252253254255256
257258259260261262263264265266267268269270271272273274275276
277278279280281282283284285286287288289290291292293294295296
297298299300301302303304305306307308309310311312313314315316
317318319320321322323324325326327328329330331332333334335336
337338339340341342343344345346347348349350351352353354355356
357358359360361362363364365366367368369370371372373374375376
377378379380381382383384385386387388389390391392393394395396
397398399400401402403404405406407408409410411412413414415416
417418419420421422423424425426427428429430431432433434435436
437438439440441442443444445446447448449450451452453454455456
457458459460461462463464465466467468469470471472473474475476
477478479480481482483484485486487488489490491492493494495496
497498499500501502503504505506507508509510511512513514515516
517518519520521522523524525526527528529530531532533534535536
537538539540541542543544545546547548549550551552553554555556
557558559560561562563564565566567568569570571572573574575576
577578579580581582583584585586587588589590591592593594595596
597598599600601602603604605606607608609610611612613614615616
617618619620621622623624625626627628629630631632633634635636
637638639640641642643644645646647648649650651652653654655656
657658659660661662663664665666667668669670671672673674675676
677678679680681682683684685686687688689690691692693694695696
697698699700701702703704705706707708709710711712713714715716
717718719720721722723724725726727728729730731732733734735736
737738739740741742743744745746747748749750751752753754755756
757758759760761762763764765766767768769770771772773774775776
777778779780781782783784785786787788789790791792793794795796
797798799800801802803804805806807808809810811812813814815816
817818819820821822823824825826827828829830831832833834835836
837838839840841842843844845846847848849850851852853854855856
857858859860861862863864865866867868869870871872873874875876
877878879880881882883884885886887888889890891892893894895896
897898899900901902903904905906907908909910911912913914915916
917918919920921922923924925926927928929930931932933934935936
937938939940941942943944945946947948949950951952953954955956
957958959960961962963964965966967968969970971972973974975976
977978979980981982983984985986987988989990991992993994995996
997998999100010011002100310041005100610071008100910101011101
210131014101510161017101810191020102110221023102410251026102
710281029103010311032103310341035103610371038103910401041104
210431044104510461047104810491050105110521053105410551056105
710581059106010611062106310641065106610671068106910701071107
210731074107510761077107810791080108110821083108410851086108
710881089109010911092109310941095109610971098109911001101110
211031104110511061107110811091110111111121113111411151116111
711181119112011211122112311241125112611271128112911301131113
211331134113511361137113811391140114111421143114411451146114
711481149115011511152115311541155115611571158115911601161116
211631164116511661167116811691170117111721173117411751176117
711781179118011811182118311841185118611871188118911901191119
211931194119511961197119811991200120112021203120412051206120
712081209121012111212121312141215121612171218121912201221122
212231224122512261227122812291230123112321233123412351236123
712381239124012411242124312441245124612471248124912501251125
212531254125512561257125812591260126112621263126412651266126
712681269127012711272127312741275127612771278127912801281128
212831284128512861287128812891290129112921293129412951296129
712981299130013011302130313041305130613071308130913101311131
213131314131513161317131813191320132113221323132413251326132
713281329133013311332133313341335133613371338133913401341134
213431344134513461347134813491350135113521353135413551356135
713581359136013611362136313641365136613671368136913701371137
213731374137513761377137813791380138113821383138413851386138
713881389139013911392139313941395139613971398139914001401140
214031404140514061407140814091410141114121413141414151416141
714181419142014211422142314241425142614271428142914301431143
214331434143514361437143814391440144114421443144414451446144
714481449145014511452145314541455145614571458145914601461146
214631464146514661467146814691470147114721473147414751476147
714781479148014811482148314841485148614871488148914901491149
214931494149514961497149814991500150115021503150415051506150
715081509151015111512151315141515151615171518151915201521152
215231524152515261527152815291530153115321533153415351536153
715381539154015411542154315441545154615471548154915501551155
215531554155515561557155815591560156115621563156415651566156
715681569157015711572157315741575157615771578157915801581158
215831584158515861587158815891590159115921593159415951596159
715981599160016011602160316041605160616071608160916101611161
216131614161516161617161816191620162116221623162416251626162
716281629163016311632163316341635163616371638163916401641164
216431644164516461647164816491650165116521653165416551656165
716581659166016611662166316641665166616671668166916701671167
216731674167516761677167816791680168116821683168416851686168
716881689169016911692169316941695169616971698169917001701170
217031704170517061707170817091710171117121713171417151716171
717181719172017211722172317241725172617271728172917301731173
217331734173517361737173817391740174117421743174417451746174
717481749175017511752175317541755175617571758175917601761176
217631764176517661767176817691770177117721773177417751776177
717781779178017811782178317841785178617871788178917901791179
217931794179517961797179817991800180118021803180418051806180
718081809181018111812181318141815181618171818181918201821182
218231824182518261827182818291830183118321833183418351836183
718381839184018411842184318441845184618471848184918501851185
218531854185518561857185818591860186118621863186418651866186
718681869187018711872187318741875187618771878187918801881188
218831884188518861887188818891890189118921893189418951896189
718981899190019011902190319041905190619071908190919101911191
219131914191519161917191819191920192119221923192419251926192
719281929193019311932193319341935193619371938193919401941194
219431944194519461947194819491950195119521953195419551956195
719581959196019611962196319641965196619671968196919701971197
219731974197519761977197819791980198119821983198419851986198
719881989199019911992199319941995199619971998199920002001200
220032004200520062007200820092010201120122013201420152016201
720182019202020212022202320242025202620272028202920302031203
220332034203520362037203820392040204120422043204420452046204
720482049205020512052205320542055205620572058205920602061206
220632064206520662067206820692070207120722073207420752076207
720782079208020812082208320842085208620872088208920902091209
220932094209520962097209820992100210121022103210421052106210
721082109211021112112211321142115211621172118211921202121212
221232124212521262127212821292130213121322133213421352136213
721382139214021412142214321442145214621472148214921502151215
221532154215521562157215821592160216121622163216421652166216
721682169217021712172217321742175217621772178217921802181218
221832184218521862187218821892190219121922193219421952196219
721982199220022012202220322042205220622072208220922102211221
222132214221522162217221822192220222122222223222422252226222
722282229223022312232223322342235223622372238223922402241224
222432244224522462247224822492250225122522253225422552256225
722582259226022612262226322642265226622672268226922702271227
222732274227522762277227822792280228122822283228422852286228
722882289229022912292229322942295229622972298229923002301230
223032304230523062307230823092310231123122313231423152316231
723182319232023212322232323242325232623272328232923302331233
223332334233523362337233823392340234123422343234423452346234
723482349235023512352235323542355235623572358235923602361236
223632364236523662367236823692370237123722373237423752376237
723782379238023812382238323842385238623872388238923902391239
223932394239523962397239823992400240124022403240424052406240
724082409241024112412241324142415241624172418241924202421242
224232424242524262427242824292430243124322433243424352436243
724382439244024412442244324442445244624472448244924502451245
224532454245524562457245824592460246124622463246424652466246
724682469247024712472247324742475247624772478247924802481248
224832484248524862487248824892490249124922493249424952496249
724982499250025012502250325042505250625072508250925102511251
225132514251525162517251825192520252125222523252425252526252
725282529253025312532253325342535253625372538253925402541254
225432544254525462547254825492550255125522553255425552556255
725582559256025612562256325642565256625672568256925702571257
225732574257525762577257825792580258125822583258425852586258
725882589259025912592259325942595259625972598259926002601260
226032604260526062607260826092610261126122613261426152616261
726182619262026212622262326242625262626272628262926302631263
226332634263526362637263826392640264126422643264426452646264
726482649265026512652265326542655265626572658265926602661266
226632664266526662667266826692670267126722673267426752676267
726782679268026812682268326842685268626872688268926902691269
226932694269526962697269826992700270127022703270427052706270
727082709271027112712271327142715271627172718271927202721272
227232724272527262727272827292730273127322733273427352736273
727382739274027412742274327442745274627472748274927502751275
227532754275527562757275827592760276127622763276427652766276
727682769277027712772277327742775277627772778277927802781278
227832784278527862787278827892790279127922793279427952796279
727982799280028012802280328042805280628072808280928102811281
228132814281528162817281828192820282128222823282428252826282
728282829283028312832283328342835283628372838283928402841284
228432844284528462847284828492850285128522853285428552856285
728582859286028612862286328642865286628672868286928702871287
228732874287528762877287828792880288128822883288428852886288
728882889289028912892289328942895289628972898289929002901290
229032904290529062907290829092910291129122913291429152916291
729182919292029212922292329242925292629272928292929302931293
229332934293529362937293829392940294129422943294429452946294
729482949295029512952295329542955295629572958295929602961296
229632964296529662967296829692970297129722973297429752976297
729782979298029812982298329842985298629872988298929902991299
229932994299529962997299829993000300130023003300430053006300
730083009301030113012301330143015301630173018301930203021302
230233024302530263027302830293030303130323033303430353036303
730383039304030413042304330443045304630473048304930503051305
230533054305530563057305830593060306130623063306430653066306
730683069307030713072307330743075307630773078307930803081308
230833084308530863087308830893090309130923093309430953096309
730983099310031013102310331043105310631073108310931103111311
231133114311531163117311831193120312131223123312431253126312
731283129313031313132313331343135313631373138313931403141314
231433144314531463147314831493150315131523153315431553156315
731583159316031613162316331643165316631673168316931703171317
231733174317531763177317831793180318131823183318431853186318
731883189319031913192319331943195319631973198319932003201320
232033204320532063207320832093210321132123213321432153216321
732183219322032213222322332243225322632273228322932303231323
232333234323532363237323832393240324132423243324432453246324
732483249325032513252325332543255325632573258325932603261326
232633264326532663267326832693270327132723273327432753276327
732783279328032813282328332843285328632873288328932903291329
232933294329532963297329832993300330133023303330433053306330
733083309331033113312331333143315331633173318331933203321332
233233324332533263327332833293330333133323333333433353336333
733383339334033413342334333443345334633473348334933503351335
233533354335533563357335833593360336133623363336433653366336
733683369337033713372337333743375337633773378337933803381338
233833384338533863387338833893390339133923393339433953396339
733983399340034013402340334043405340634073408340934103411341
234133414341534163417341834193420342134223423342434253426342
734283429343034313432343334343435343634373438343934403441344
234433444344534463447344834493450345134523453345434553456345
734583459346034613462346334643465346634673468346934703471347
234733474347534763477347834793480348134823483348434853486348
734883489349034913492349334943495349634973498349935003501350
235033504350535063507350835093510351135123513351435153516351
735183519352035213522352335243525352635273528352935303531353
235333534353535363537353835393540354135423543354435453546354
735483549355035513552355335543555355635573558355935603561356
235633564356535663567356835693570357135723573357435753576357
735783579358035813582358335843585358635873588358935903591359
235933594359535963597359835993600360136023603360436053606360
736083609361036113612361336143615361636173618361936203621362
236233624362536263627362836293630363136323633363436353636363
736383639364036413642364336443645364636473648364936503651365
236533654365536563657365836593660366136623663366436653666366
736683669367036713672367336743675367636773678367936803681368
236833684368536863687368836893690369136923693369436953696369
736983699370037013702370337043705370637073708370937103711371
237133714371537163717371837193720372137223723372437253726372
737283729373037313732373337343735373637373738373937403741374
237433744374537463747374837493750375137523753375437553756375
737583759376037613762376337643765376637673768376937703771377
237733774377537763777377837793780378137823783378437853786378
737883789379037913792379337943795379637973798379938003801380
238033804380538063807380838093810381138123813381438153816381
738183819382038213822382338243825382638273828382938303831383
238333834383538363837383838393840384138423843384438453846384
738483849385038513852385338543855385638573858385938603861386
238633864386538663867386838693870387138723873387438753876387
738783879388038813882388338843885388638873888388938903891389
238933894389538963897389838993900390139023903390439053906390
739083909391039113912391339143915391639173918391939203921392
239233924392539263927392839293930393139323933393439353936393
739383939394039413942394339443945394639473948394939503951395
239533954395539563957395839593960396139623963396439653966396
739683969397039713972397339743975397639773978397939803981398
239833984398539863987398839893990399139923993399439953996399
739983999400040014002400340044005400640074008400940104011401
240134014401540164017401840194020402140224023402440254026402
740284029403040314032403340344035403640374038403940404041404
240434044404540464047404840494050405140524053405440554056405
740584059406040614062406340644065406640674068406940704071407
240734074407540764077407840794080408140824083408440854086408
740884089409040914092409340944095409640974098409941004101410
241034104410541064107410841094110411141124113411441154116411
741184119412041214122412341244125412641274128412941304131413
241334134413541364137413841394140414141424143414441454146414
741484149415041514152415341544155415641574158415941604161416
241634164416541664167416841694170417141724173417441754176417
741784179418041814182418341844185418641874188418941904191419
241934194419541964197419841994200420142024203420442054206420
742084209421042114212421342144215421642174218421942204221422
242234224422542264227422842294230423142324233423442354236423
742384239424042414242424342444245424642474248424942504251425
242534254425542564257425842594260426142624263426442654266426
742684269427042714272427342744275427642774278427942804281428
242834284428542864287428842894290429142924293429442954296429
742984299430043014302430343044305430643074308430943104311431
243134314431543164317431843194320432143224323432443254326432
743284329433043314332433343344335433643374338433943404341434
243434344434543464347434843494350435143524353435443554356435
743584359436043614362436343644365436643674368436943704371437
243734374437543764377437843794380438143824383438443854386438
743884389439043914392439343944395439643974398439944004401440
244034404440544064407440844094410441144124413441444154416441
744184419442044214422442344244425442644274428442944304431443
244334434443544364437443844394440444144424443444444454446444
744484449445044514452445344544455445644574458445944604461446
244634464446544664467446844694470447144724473447444754476447
744784479448044814482448344844485448644874488448944904491449
244934494449544964497449844994500450145024503450445054506450
745084509451045114512451345144515451645174518451945204521452
245234524452545264527452845294530453145324533453445354536453
745384539454045414542454345444545454645474548454945504551455
245534554455545564557455845594560456145624563456445654566456
745684569457045714572457345744575457645774578457945804581458
245834584458545864587458845894590459145924593459445954596459
745984599460046014602460346044605460646074608460946104611461
246134614461546164617461846194620462146224623462446254626462
746284629463046314632463346344635463646374638463946404641464
246434644464546464647464846494650465146524653465446554656465
746584659466046614662466346644665466646674668466946704671467
246734674467546764677467846794680468146824683468446854686468
746884689469046914692469346944695469646974698469947004701470
247034704470547064707470847094710471147124713471447154716471
747184719472047214722472347244725472647274728472947304731473
247334734473547364737473847394740474147424743474447454746474
747484749475047514752475347544755475647574758475947604761476
247634764476547664767476847694770477147724773477447754776477
747784779478047814782478347844785478647874788478947904791479
247934794479547964797479847994800480148024803480448054806480
748084809481048114812481348144815481648174818481948204821482
248234824482548264827482848294830483148324833483448354836483
748384839484048414842484348444845484648474848484948504851485
248534854485548564857485848594860486148624863486448654866486
748684869487048714872487348744875487648774878487948804881488
248834884488548864887488848894890489148924893489448954896489
748984899490049014902490349044905490649074908490949104911491
249134914491549164917491849194920492149224923492449254926492
749284929493049314932493349344935493649374938493949404941494
249434944494549464947494849494950495149524953495449554956495
749584959496049614962496349644965496649674968496949704971497
249734974497549764977497849794980498149824983498449854986498
74988498949904991499249934994499549964997499849995000
For the digit sequence, unless someone has found one larger, it would be
Row 567:
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012345678901234567890
123456789012345678901234567
The next would have to be beyond row 1000, and greater than
12345678901234567890123456789012345678901234567890123456789012
34567890123456789012345678901234567890123456789012345678901234
56789012345678901234567890123456789012345678901234567890123456
78901234567890123456789012345678901234567890123456789012345678
90123456789012345678901234567890123456789012345678901234567890
12345678901234567890123456789012345678901234567890123456789012
34567890123456789012345678901234567890123456789012345678901234
56789012345678901234567890123456789012345678901234567890123456
78901234567890123456789012345678901234567890123456789012345678
90123456789012345678901234567890123456789012345678901234567890
12345678901234567890123456789012345678901234567890123456789012
34567890123456789012345678901234567890123456789012345678901234
56789012345678901234567890123456789012345678901234567890123456
78901234567890123456789012345678901234567890123456789012345678
90123456789012345678901234567890123456789012345678901234567890
12345678901234567890123456789012345678901234567890123456789012
34567890
Integer sequences
On a mailing list, my attention was caught by a comment,
Daniel Dockery, please help me find better sequences.
Unable, or at least unwilling, to resist, I offered the following integer sequence:
7
47
247
1247
6247
31247
156247
781247
3906247
19531247
97656247
488281247
2441406247
12207031247
61035156247
305175781247
1525878906247
7629394531247
38146972656247
190734863281247
953674316406247
4768371582031247
23841857910156247
119209289550781247
596046447753906247
2980232238769531247
14901161193847656247
74505805969238281247
372529029846191406247
1862645149230957031247
9313225746154785156247
46566128730773925781247
232830643653869628906247
1164153218269348144531247
5820766091346740722656247
29103830456733703613281247
145519152283668518066406247
727595761418342590332031247
3637978807091712951660156247
18189894035458564758300781247
90949470177292823791503906247
454747350886464118957519531247
2273736754432320594787597656247
11368683772161602973937988281247
56843418860808014869689941406247
284217094304040074348449707031247
1421085471520200371742248535156247
7105427357601001858711242675781247
35527136788005009293556213378906247
177635683940025046467781066894531247
888178419700125232338905334472656247
4440892098500626161694526672363281247
22204460492503130808472633361816406247
111022302462515654042363166809082031247
555111512312578270211815834045410156247
2775557561562891351059079170227050781247
13877787807814456755295395851135253906247
69388939039072283776476979255676269531247
346944695195361418882384896278381347656247
1734723475976807094411924481391906738281247
8673617379884035472059622406959533691406247
43368086899420177360298112034797668457031247
216840434497100886801490560173988342285156247
1084202172485504434007452800869941711425781247
5421010862427522170037264004349708557128906247
27105054312137610850186320021748542785644531247
135525271560688054250931600108742713928222656247
677626357803440271254658000543713569641113281247
3388131789017201356273290002718567848205566406247
16940658945086006781366450013592839241027832031247
84703294725430033906832250067964196205139160156247
423516473627150169534161250339820981025695800781247
2117582368135750847670806251699104905128479003906247
10587911840678754238354031258495524525642395019531247
52939559203393771191770156292477622628211975097656247
264697796016968855958850781462388113141059875488281247
1323488980084844279794253907311940565705299377441406247
6617444900424221398971269536559702828526496887207031247
33087224502121106994856347682798514142632484436035156247
165436122510605534974281738413992570713162422180175781247
827180612553027674871408692069962853565812110900878906247
4135903062765138374357043460349814267829060554504394531247
20679515313825691871785217301749071339145302772521972656247
103397576569128459358926086508745356695726513862609863281247
516987882845642296794630432543726783478632569313049316406247
2584939414228211483973152162718633917393162846565246582031247
12924697071141057419865760813593169586965814232826232910156247
64623485355705287099328804067965847934829071164131164550781247
323117426778526435496644020339829239674145355820655822753906247
1615587133892632177483220101699146198370726779103279113769531247
8077935669463160887416100508495730991853633895516395568847656247
40389678347315804437080502542478654959268169477581977844238281247
201948391736579022185402512712393274796340847387909889221191406247
1009741958682895110927012563561966373981704236939549446105957031247
5048709793414475554635062817809831869908521184697747230529785156247
25243548967072377773175314089049159349542605923488736152648925781247
126217744835361888865876570445245796747713029617443680763244628906247
631088724176809444329382852226228983738565148087218403816223144531247
3155443620884047221646914261131144918692825740436092019081115722656247
15777218104420236108234571305655724593464128702180460095405578613281247
The last digit remains 7; for numbers of more than one digit, the final two digits remain 47; for numbers with more than two digits, the final three remain 247. For numbers of more than three digits, the fourth-to-the-last digit alternates between 1 and 6 (1 for even x [see below, for how to generate the sequence, to see what I mean by x], 6 for odd). For numbers of more than four digits, the fifth-to-the-last digit repeats the sequence: 3, 5, 8, 0. More than five digits, and the sixth-to-last digit repeats: 1, 7, 9, 5, 6, 2, 4, 0. More than six, the seventh-to-last repeats: 3, 9, 7, 8, 1, 7, 5, 5, 8, 4, 2, 3, 6, 2, 0, 0. And so on.
How is it derived? Let p(n,k) designate the nth polygonal number p of the set of polygonal numbers for a k-sided polygon. E.g., p(n,3) would reveal the triangular numbers, p(n,4) the squares, etc. You can define the function in pari with
p(n,k) = (n/2)*(n*k-k+4-2*n)
or in Maple with
p := proc(n,k) (n/2)*(n*k-k+4-2*n) end:
The sequence is generated simply by taking p(5,5x)/5 for x=1,2,3…n (n was stopped arbitrarily at 100 in the above example list).
p(5,5x) ÷ 5 for 1 ≤ x ≤ 120If you want to skip the polygonal number function altogether, you can render the above sequence with f(x) = 2*5x-3. I included the reference to the polygonal numbers simply to show the source from which I derived the sequence.
In response to the same person having asked about an æsthetically pleasing sequence (to me), I came up with this:
1001001
101101101101
10111111111111101
1011112112112112111101
101111212212212212212111101
10111121222222222222222212111101
1011112122223223223223223222212111101
101111212222323323323323323323222212111101
10111121222232333333333333333333323222212111101
1011112122223233334334334334334334333323222212111101
101111212222323333434434434434434434434333323222212111101
10111121222232333343444444444444444444444434333323222212111101
1011112122223233334344445445445445445445445444434333323222212111101
101111212222323333434444545545545545545545545545444434333323222212111101
... etc. ...
If you define a generalized function f(x,y) → ((10^x)^y - 1) / (10^x - 1), then you can generate the above by evaluating f(3,y) × f(2,y-1) for successive values of y > 2.
In case the “jumble” of numbers aren’t very clear for some, I rendered a quick image of the sequence colored to show the distribution of prime digits: white areas (inside the general triangle shape) represent non-primes, black areas are the digits 0 and 1; primes are in red.
f(3,y) × f(2,y-1)
