login
A063611
Smallest k such that 7^k has exactly n 5's in its decimal representation.
0
1, 7, 15, 27, 21, 49, 55, 47, 51, 87, 85, 107, 75, 99, 61, 149, 138, 133, 171, 135, 165, 237, 209, 197, 269, 221, 232, 219, 277, 248, 258, 306, 271, 264, 357, 296, 310, 347, 354, 260, 342, 374, 407, 425, 362, 457, 485, 480, 486, 488, 492
OFFSET
0,2
MATHEMATICA
a = {}; Do[k = 1; While[ Count[ IntegerDigits[7^k], 5] != n, k++ ]; a = Append[a, k], {n, 0, 50} ]; a
Join[{1}, With[{p7=7^Range[0, 500]}, Flatten[Table[Position[p7, _?(DigitCount[ #, 10, 5]==n&), {1}, 1], {n, 50}]]-1]] (* Harvey P. Dale, Sep 17 2013 *)
CROSSREFS
Sequence in context: A154935 A012480 A226470 * A292379 A146624 A239934
KEYWORD
base,nonn
AUTHOR
Robert G. Wilson v, Aug 10 2001
EXTENSIONS
Name corrected by Jon E. Schoenfield, Jun 26 2018
STATUS
approved