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 A063606 #11 Apr 12 2022 09:22:58
%S A063606 0,4,9,13,25,55,39,41,45,70,69,65,75,107,109,134,167,142,156,196,157,
%T A063606 205,214,180,213,183,162,251,263,276,268,290,306,295,369,313,332,293,
%U A063606 353,340,357,387,367,476,334,509,363,474,454,488,453
%N A063606 Smallest k >= 0 such that 7^k has exactly n 0's in its decimal representation.
%t A063606 a = {}; Do[k = 0; While[ Count[ IntegerDigits[7^k], 0] != n, k++ ]; a = Append[a, k], {n, 0, 50} ]; a
%t A063606 Module[{p7=DigitCount[#,10,0]&/@(7^Range[600]),nn=60},Join[{0},Flatten[ Table[ Position[p7,n,1,1],{n,nn}]]]] (* _Harvey P. Dale_, Apr 12 2022 *)
%o A063606 (PARI) A063606(n)=for(k=n, oo, #select(d->!d, digits(5^k))==n&&return(k)) \\ _M. F. Hasler_, Jun 14 2018
%Y A063606 Cf. A031146 (analog for 2^k), A063555 (analog for 3^k), A063575 (analog for 4^k), A063585 (for 5^k), A063596 (analog for 6^k).
%K A063606 base,nonn
%O A063606 0,2
%A A063606 _Robert G. Wilson v_, Aug 10 2001