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 A113072 #6 Jan 30 2021 08:44:11 %S A113072 1,2,2,1,4,3,0,2,6,4,0,0,3,8,5,0,0,0,4,10,6,0,0,0,0,5,12,7,0,0,0,0,0, %T A113072 6,14,8,0,0,0,0,0,0,7,16,9,0,0,0,0,0,0,0,8,18,10,0,0,0,0,0,0,0,0,9,20, %U A113072 11,0,0,0,0,0,0,0,0,0,10,22,12,0,0,0,0,0,0,0,0,0,0,11,24,13,0,0,0,0,0,0,0 %N A113072 Tridiagonal matrix associated with coordination sequences. %C A113072 Coefficient array of expansion of ((1+x)/(1-r*x))^2, or self-convolution of coordination sequence for the infinite tree with valency r. Row sums are A008574, (coordination sequence for square lattice). Diagonal sums are A000027. %F A113072 Column k has g.f. (1+x)^2*(k+1)x^k. %e A113072 Triangle begins %e A113072 1; %e A113072 2, 2; %e A113072 1, 4, 3; %e A113072 0, 2, 6, 4; %e A113072 0, 0, 3, 8, 5; %e A113072 0, 0, 0, 4, 10, 6; %e A113072 0, 0, 0, 0, 5, 12, 7; %Y A113072 Cf. A113070, A113071. %K A113072 easy,nonn,tabl %O A113072 0,2 %A A113072 _Paul Barry_, Oct 14 2005