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 A126013 #4 Mar 31 2012 13:21:13 %S A126013 0,1,2,3,4,0,5,0,0,6,0,0,7,0,0,0,0,0,8,0,0,0,0,0,0,0,0,0,0,0,0,0,9,10, %T A126013 0,0,11,0,0,0,0,0,0,0,0,0,0,0,12,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,13, %U A126013 14,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,15,16,0,0 %N A126013 Inverse function of N->N injection A126011. %C A126013 a(0)=0 because A126011(0)=0, but a(n) = 0 also for those n which do not occur as values of A126011. All positive natural numbers occur here once. %H A126013 A. Karttunen, <a href="/A126000/a126000.scm.txt">Scheme-program for computing this sequence.</a> %Y A126013 a(A126011(n)) = n for all n. %K A126013 nonn %O A126013 0,3 %A A126013 _Antti Karttunen_, Dec 18 2006