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 A117138 #3 Mar 30 2012 16:50:24 %S A117138 0,0,0,1,3,0,0,2,5,1,6,0,0,3,7,2,8,1,9,0,0,4,9,3,10,2,11,1,12,0,0,5, %T A117138 11,4,12,3,13,2,14,1,15,0,0,6,13,5,14,4,15,3,16,2,17,1,18,0 %N A117138 Similar to A117136 but begin each row with 0. Equals A117136 - 1. %K A117138 nonn,tabf %O A117138 0,5 %A A117138 _N. J. A. Sloane_, Apr 21 2006