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A063610
Smallest k such that 7^k has exactly n 4's in its decimal representation.
1
1, 2, 10, 15, 26, 32, 33, 58, 62, 50, 46, 89, 102, 108, 90, 118, 130, 122, 146, 144, 112, 138, 196, 224, 226, 212, 256, 250, 259, 239, 218, 254, 386, 260, 318, 292, 353, 321, 358, 326, 392, 401, 330, 396, 427, 442, 438, 443, 450, 449, 474
OFFSET
0,2
MATHEMATICA
a = {}; Do[k = 1; While[ Count[ IntegerDigits[7^k], 4] != n, k++ ]; a = Append[a, k], {n, 0, 50} ]; a
Module[{nn=50, p7s}, p7s=Table[DigitCount[7^n, 10, 4], {n, 20nn}]; Join[{1}, Table[ Position[p7s, i, {1}, 1], {i, nn}]]]//Flatten (* Harvey P. Dale, Jun 13 2016 *)
CROSSREFS
Sequence in context: A272041 A212160 A134861 * A369650 A181474 A047187
KEYWORD
base,nonn
AUTHOR
Robert G. Wilson v, Aug 10 2001
EXTENSIONS
Name corrected by Jon E. Schoenfield, Jun 26 2018
STATUS
approved