cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-3 of 3 results.

A035064 Numbers k such that 2^k does not contain the digit 9 (probably finite).

Original entry on oeis.org

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 14, 15, 16, 17, 18, 19, 20, 23, 24, 25, 26, 27, 28, 30, 31, 45, 46, 47, 57, 58, 59, 71, 77, 99, 108
Offset: 1

Views

Author

Patrick De Geest, Nov 15 1998

Keywords

Examples

			Here is 2^108, conjecturally the largest power of 2 that does not contain a 9: 324518553658426726783156020576256. - _N. J. A. Sloane_, Feb 10 2023

Crossrefs

Cf. numbers n such that decimal expansion of 2^n contains no k: A007377 (k=0), A035057 (k=1), A034293 (k=2), A035058 (k=3), A035059 (k=4), A035060 (k=5), A035061 (k=6), A035062 (k=7), A035063 (k=8), this sequence (k=9).
Indices of zeros in A065744 (number of 9s in digits of 2^n).

Programs

Extensions

Initial 0 added by Vincenzo Librandi, May 06 2015
Removed keyword "fini" at the suggestion of Nathan Fox, since it is only a conjecture that this sequence contains only finitely many terms. - N. J. A. Sloane, Mar 03 2016

A065714 Number of 3's in decimal expansion of 2^n.

Original entry on oeis.org

0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0, 3, 0, 1, 1, 1, 1, 1, 0, 1, 0, 4, 1, 3, 0, 1, 0, 1, 1, 1, 0, 3, 1, 3, 0, 2, 0, 1, 2, 0, 1, 2, 2, 0, 2, 3, 0, 4, 1, 3, 1, 4, 2, 1, 1, 1, 2, 3, 2, 3, 1, 2, 4, 1, 4, 3, 0, 3, 2, 3, 4, 4, 3, 3, 2, 1, 3, 0, 0, 4, 2, 2, 6, 1, 4, 4, 2
Offset: 0

Views

Author

Benoit Cloitre, Dec 04 2001

Keywords

Comments

I conjecture that any value x = 0, 1, 2, ... occurs only a finite number of times N(x) = 34, 34, 24, 34, 39, 34, 35, 34, 35, 32, 33, 31, ... in this sequence, for the last time at well defined indices i(x) = 153, 139, 226, 237, 308, 386, 413, 506, 461, 578, 644, 732, 857, 657, 743, 768, 784, 848, 906, ... - M. F. Hasler, Jul 09 2025

Examples

			2^5 = 32 so a(5)=1.

Links

Crossrefs

Cf. A000079 (powers of 2), A035058 (2^n does not contain the digit 3).
Similar for other digits: A027870 (0's), A065712 (1's), A065710 (2's), this (3's), A065715 (4's), A065716 (5's), A065717 (6's), A065718 (7's), A065719 (8's), A065744 (9's).
Cf. A094776 (index of last occurrence of digit n in powers of 2).

Programs

  • Mathematica
    Table[ Count[ IntegerDigits[2^n], 3], {n, 0, 100} ]
  • PARI
    a(n) = #select(x->(x==3), digits(2^n)); \\ Michel Marcus, Jun 15 2018
  • Python
    def A065714(n):
    return str(2**n).count('3') # Chai Wah Wu, Feb 14 2020

Extensions

More terms from Robert G. Wilson v, Dec 07 2001

A294087 Least prime p_k such that (p_k)^n has p_{k+1} as substring.

Original entry on oeis.org

23, 11, 37, 2, 7, 5, 3, 41, 3, 13, 3, 3, 2, 2, 2, 2, 5, 5, 5, 3, 2, 2, 3, 2, 3, 2, 2, 2, 2, 2, 3, 2, 3, 2, 2, 2, 3, 2, 3, 2, 2, 2, 17, 2, 2, 2, 3, 2, 3, 2, 2, 3, 2, 2, 2, 3, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2
Offset: 2

Views

Author

Paolo P. Lava, Feb 09 2018

Keywords

Comments

It appears that a(n) = 2 for n>153. In other words, for n>153, 3 is always a substring of 2^n. Is there any proof? See A035058.

Examples

			23^2 = 529 and 29 is the prime after 23.
11^3 = 1331 and 13 is the prime after 11.
37^4 = 1874161 and 41 is the prime after 37.

Crossrefs

Cf. A035058, A052073, A052075, A294088.

Programs

  • Maple
    P:=proc(q) local a,b,h,k,n,ok; for h from 2 to q do ok:=1; for n from 1 to q do
if ok=1 then a:=ithprime(n); b:=nextprime(a); for k from 1 to ilog10(a^h)-ilog10(b)+1 do
if b=trunc(a^h/10^(k-1)) mod 10^(ilog10(b)+1) then print(a); ok:=0; break;
fi; od; fi; od; od; end: P(10^6);
Showing 1-3 of 3 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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