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 A064891 #4 Mar 30 2012 17:38:10 %S A064891 0,1,2,0,2,0,1,0,0,0,1,0,1,0,0,0,2,0,1,0,0,0,2,0,0,0,0,0,3,0,1,0,0,0, %T A064891 0,0,1,0,0,0,1,0,3,0,0,0,3,0,0,0,0,0,3,0,0,0,0,0,1,0,3,0,0,0,0,0,1,0, %U A064891 0,0,1,0,1,0,0,0,0,0,1,0,0,0,2,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,1,0,1,0,0 %N A064891 "Binary potency" of n: length of shortest blocks of 0's inserted between the bits of n required to "dilute" it into a nonprime. %C A064891 Zero for all nonprime n. Note that the +2 dilution of 3 is not the +1 dilution of 5! %e A064891 3 = 11 -> 0101 = 5 -> 001001 = 9, so a(3) = 2; 5 = 101 -> 010001 = 17 -> 001000001 = 65, so a(5) = 2 %Y A064891 Cf. A000040, A064892, A064893. %K A064891 base,easy,nonn %O A064891 1,3 %A A064891 _Marc LeBrun_, Oct 10 2001