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 A231353 #5 Nov 08 2013 14:42:22 %S A231353 0,0,1,0,1,2,0,1,-1,3,0,1,3,-1,2,0,1,4,-1,2,-1,0,1,-1,3,2,4,-1,0,1,3, %T A231353 4,2,-1,-1,5,0,1,-1,6,2,-1,6,-1,4,0,1,-1,-1,2,7,6,4,5,3,0,1,6,-1,2,-1, %U A231353 4,-1,-1,3,8,0,1,-1,-1,2,4,6,-1,8,3,-1,7,0,1,5,6,2 %N A231353 Least k>=0 such that n - k^2 is a triangular number, or -1 if no such k exists. %C A231353 Indices of -1's: A014134. %C A231353 Indices of 0's: A000217. %C A231353 Indices of 1's: A000124. %Y A231353 Cf. A000217, A000290, A014134, A000124, A231354. %K A231353 sign %O A231353 0,6 %A A231353 _Alex Ratushnyak_, Nov 08 2013