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 A166902 #2 Mar 30 2012 18:37:18
%S A166902 1,9,84,935,12480,196623,3591560,74847168,1755406674,45804773872,
%T A166902 1317004696656,41386864224420,1411592788770580,51942256939923051,
%U A166902 2051313029747633376,86548588478842559964,3885584044838123386104
%N A166902 Column 2 of triangle A166900.
%C A166902 Triangle A166900 transforms rows into diagonals in the table of coefficients of successive iterations of x+x^2 (cf. A122888).
%o A166902 (PARI) {a(n)=local(F=x, M, N, P); M=matrix(n+4, n+4, r, c, F=x;for(i=1, r+c-2, F=subst(F, x, x+x^2+x*O(x^(n+4)))); polcoeff(F, c)); N=matrix(n+3, n+3, r, c, F=x;for(i=1, r, F=subst(F, x, x+x^2+x*O(x^(n+4)))); polcoeff(F, c)); P=matrix(n+3, n+3, r, c, M[r+1, c]); (P~*N~^-1)[n+3, 3]}
%Y A166902 Cf. A166900, A166901, A166903, A122888, A135080.
%K A166902 nonn
%O A166902 0,2
%A A166902 _Paul D. Hanna_, Nov 27 2009