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 A113126 #2 Mar 30 2012 18:59:12 %S A113126 1,1,2,1,2,3,1,2,3,4,0,2,3,4,5,0,0,3,4,5,6,0,0,0,4,5,6,7,0,0,0,0,5,6, %T A113126 7,8,0,0,0,0,0,6,7,8,9,0,0,0,0,0,0,7,8,9,10,0,0,0,0,0,0,0,8,9,10,11,0, %U A113126 0,0,0,0,0,0,0,9,10,11,12,0,0,0,0,0,0,0,0,0,10,11,12,13,0,0,0,0,0,0,0,0,0,0 %N A113126 A simple 4-diagonal matrix. %C A113126 Row sums are A113127. Diagonal sums are A109613. Diagonals are A000027. %F A113126 Number triangle where column k has g.f. (1+x+x^2+x^3)(k+1)x^k. %e A113126 Triangle begins %e A113126 1; %e A113126 1,2; %e A113126 1,2,3; %e A113126 1,2,3,4; %e A113126 0,2,3,4,5; %e A113126 0,0,3,4,5,6; %e A113126 0,0,0,4,5,6,7; %e A113126 0,0,0,0,5,6,7,8; %e A113126 0,0,0,0,0,6,7,8,9; %Y A113126 Cf. A113125. %K A113126 easy,nonn,tabl %O A113126 0,3 %A A113126 _Paul Barry_, Oct 14 2005