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A063608
Smallest k such that 7^k has exactly n 2's in its decimal representation.
0
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
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
KEYWORD
base,nonn
AUTHOR
Robert G. Wilson v, Aug 10 2001
EXTENSIONS
Name corrected by Jon E. Schoenfield, Jun 26 2018
STATUS
approved