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 A121241 #4 Sep 08 2013 13:30:53 %S A121241 1,1,1,-1,-1,1,-1,1,-1,1,1,-1,1,-1,-1,1,-1,1,1,-1,-1,1,-1,1,1,-1,1,-1, %T A121241 1,-1,-1,1,-1,1,1,-1,-1,1,-1,1,-1,1,1,-1,1,-1,-1,1,1,-1,1,-1,-1,1,-1, %U A121241 1,1,-1,1,-1,1,-1,-1,1,-1,1,1,-1,-1,1,-1,1,-1,1,1,-1,1,-1,-1,1,-1,1,1,-1,-1,1,-1,1,1,-1,1,-1,1,-1,-1,1,1,-1,1,-1,-1,1,-1 %N A121241 Change 0 to -1 in A090678. %F A121241 a(n) = (-1)^(1+A088567(n)). %K A121241 sign %O A121241 0,1 %A A121241 _Philippe Deléham_, Aug 22 2006