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 A181520 #3 Mar 30 2012 18:52:59 %S A181520 1,1,3,3,3,1,3,3,3,3,3,3,3,5,3,3,3,5,1,3,3,3,3,5,3,3,3,5,5,3,3,3,5,3, %T A181520 5,5,3,5,5,5,3,3,3,5,5,5,7,5,5,5,5,5,7,5,7,3,3,3,5,5,5,7,3,3,5,5,5,5, %U A181520 3,5,5,7,5,5,7,7,7,3,3,3,7,3,5,5,7,5,7,7,7,5,7,7,7,9,3,3,3,5,3,3,3,3,5,5,3 %N A181520 2*A181518(n)-A181516(n). %K A181520 nonn %O A181520 1,3 %A A181520 _Vladimir Shevelev_, Oct 26 2010 %E A181520 More terms from _R. J. Mathar_, Nov 04 2010