This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A063610 #12 Apr 22 2025 14:07:09
%S A063610 1,2,10,15,26,32,33,58,62,50,46,89,102,108,90,118,130,122,146,144,112,
%T A063610 138,196,224,226,212,256,250,259,239,218,254,386,260,318,292,353,321,
%U A063610 358,326,392,401,330,396,427,442,438,443,450,449,474
%N A063610 Smallest k such that 7^k has exactly n 4's in its decimal representation.
%H A063610 Robert Price, <a href="/A063610/b063610.txt">Table of n, a(n) for n = 0..2000</a>
%t A063610 a = {}; Do[k = 1; While[ Count[ IntegerDigits[7^k], 4] != n, k++ ]; a = Append[a, k], {n, 0, 50} ]; a
%t A063610 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 *)
%K A063610 base,nonn
%O A063610 0,2
%A A063610 _Robert G. Wilson v_, Aug 10 2001
%E A063610 Name corrected by _Jon E. Schoenfield_, Jun 26 2018