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 A166903 #2 Mar 30 2012 18:37:18
%S A166903 1,16,230,3564,61845,1207696,26415840,642448632,17240108314,
%T A166903 506777596248,16210958231104,560988459704192,20891752852722701,
%U A166903 833382707754108896,35461362393617267808,1603581518693484768464
%N A166903 Column 3 of triangle A166900.
%C A166903 Triangle A166900 transforms rows into diagonals in the table of coefficients of successive iterations of x+x^2 (cf. A122888).
%o A166903 (PARI) {a(n)=local(F=x, M, N, P); M=matrix(n+5, n+5, r, c, F=x;for(i=1, r+c-2, F=subst(F, x, x+x^2+x*O(x^(n+5)))); polcoeff(F, c)); N=matrix(n+4, n+4, r, c, F=x;for(i=1, r, F=subst(F, x, x+x^2+x*O(x^(n+5)))); polcoeff(F, c)); P=matrix(n+4, n+4, r, c, M[r+1, c]); (P~*N~^-1)[n+4, 4]}
%Y A166903 Cf. A166900, A166901, A166902, A166904, A122888, A135080.
%K A166903 nonn
%O A166903 0,2
%A A166903 _Paul D. Hanna_, Nov 27 2009