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
KEYWORD
base,nonn
AUTHOR
Robert G. Wilson v, Aug 10 2001
EXTENSIONS
Name corrected by Jon E. Schoenfield, Jun 26 2018
STATUS
approved