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 A062521 #3 Mar 30 2012 17:30:32
%S A062521 5,0,4,7,1,4,2,10,7,6,5,20,25,35,9,29,2,17,15,11,28,9,36,29,5,4,9,19,
%T A062521 24,16,11,37,38,43,35,14,8,15,7,21,6,11,16,11,9,14,21,18,10,16,26,20,
%U A062521 30,8,14,8,4,10,25,22,22,29,9,7,3,8,23,12,14,17,23,13,12,15,15,22
%N A062521 4^a(n) is smallest nonnegative power of 4 containing the string 'n'.
%t A062521 Table[k = 0; While[ StringPosition[ ToString[4^k], ToString[n] ] == {}, k++ ]; k, {n, 0, 75} ]
%Y A062521 Cf. A030000. Essentially the same as A063567.
%K A062521 base,nonn
%O A062521 0,1
%A A062521 _Robert G. Wilson v_, Jun 24 2001