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 A131228 #4 Mar 30 2012 17:25:21 %S A131228 1,3,4,1,3,7,3,1,3,10,1,3,1,3,13,3,1,3,1,3,16,1,3,1,3,1,3,19,3,1,3,1, %T A131228 3,1,3,22,1,3,1,3,1,3,25,3,1,3,1,3,1,3,1,3,28 %N A131228 3*A051340 - 2*A128174. %C A131228 Row sums = A131229. %F A131228 3*A051340 - 2*A128174 as infinite lower triangular matrices. %e A131228 First few rows of the triangle are: %e A131228 1; %e A131228 3, 4; %e A131228 1, 3, 7; %e A131228 3, 1, 3, 10; %e A131228 1, 3, 1, 3, 13; %e A131228 ... %Y A131228 Cf. A051340, A128174, A131229, A131227. %K A131228 nonn %O A131228 0,2 %A A131228 _Gary W. Adamson_, Jun 20 2007