A063608 Smallest k such that 7^k has exactly n 2's in its decimal representation.

1, 4, 12, 10, 20, 32, 30, 68, 49, 73, 82, 93, 125, 103, 109, 131, 146, 119, 161, 113, 172, 163, 191, 197, 199, 240, 232, 243, 210, 217, 288, 317, 292, 289, 321, 333, 319, 327, 276, 374, 358, 397, 354, 357, 373, 452, 428, 489, 391, 516, 470

Offset

0,2

Links

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

Mathematica

a = {}; Do[k = 1; While[ Count[ IntegerDigits[7^k], 2] != n, k++ ]; a = Append[a, k], {n, 0, 50} ]; a
With[{pwrs=7^Range[600]}, Log[7, #]&/@Table[SelectFirst[pwrs, DigitCount[ #, 10, 2] == n&], {n, 0, 50}]] (* The program uses the SelectFirst function from Mathematica version 10 *) (* Harvey P. Dale, Aug 25 2015 *)

Crossrefs

Sequence in context: A247327 A348419 A238581 * A074258 A253137 A120213

Adjacent sequences: A063605 A063606 A063607 * A063609 A063610 A063611

Keyword

base,nonn

Author

Robert G. Wilson v, Aug 10 2001

Extensions

Name corrected by Jon E. Schoenfield, Jun 26 2018

Status

approved