A063606 Smallest k >= 0 such that 7^k has exactly n 0's in its decimal representation.

0, 4, 9, 13, 25, 55, 39, 41, 45, 70, 69, 65, 75, 107, 109, 134, 167, 142, 156, 196, 157, 205, 214, 180, 213, 183, 162, 251, 263, 276, 268, 290, 306, 295, 369, 313, 332, 293, 353, 340, 357, 387, 367, 476, 334, 509, 363, 474, 454, 488, 453

Offset

0,2

Links

Table of n, a(n) for n=0..50.

Mathematica

a = {}; Do[k = 0; While[ Count[ IntegerDigits[7^k], 0] != n, k++ ]; a = Append[a, k], {n, 0, 50} ]; a
Module[{p7=DigitCount[#, 10, 0]&/@(7^Range[600]), nn=60}, Join[{0}, Flatten[ Table[ Position[p7, n, 1, 1], {n, nn}]]]] (* Harvey P. Dale, Apr 12 2022 *)

Prog

(PARI) A063606(n)=for(k=n, oo, #select(d->!d, digits(5^k))==n&&return(k)) \\ M. F. Hasler, Jun 14 2018

Crossrefs

Cf. A031146 (analog for 2^k), A063555 (analog for 3^k), A063575 (analog for 4^k), A063585 (for 5^k), A063596 (analog for 6^k).

Sequence in context: A048261 A340771 A333848 * A033287 A041323 A319217

Adjacent sequences: A063603 A063604 A063605 * A063607 A063608 A063609

Keyword

base,nonn

Author

Robert G. Wilson v, Aug 10 2001

Status

approved