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 A166906 #2 Mar 30 2012 18:37:18
%S A166906 1,4,33,380,5510,95732,1933288,44437080,1144564278,32638644236,
%T A166906 1020503373032,34708182795156,1275532011982176,50365443858930384,
%U A166906 2126358227959866224,95577781657788563192,4556923094838105968302
%N A166906 Column 1 of triangle A166905.
%C A166906 Triangle A166905 transforms rows into diagonals in the table A158825 of coefficients in successive iterations of x*Catalan(x) (cf. A000108).
%o A166906 (PARI) {a(n)=local(F=x, G=serreverse(x-x^2+O(x^(n+4))), M, N, P, m=n); M=matrix(m+3, m+3, r, c, F=x;for(i=1, r+c-2, F=subst(F, x, G+x*O(x^(m+3)))); polcoeff(F, c)); N=matrix(m+2, m+2, r, c, F=x;for(i=1, r, F=subst(F, x, G+x*O(x^(m+3)))); polcoeff(F, c)); P=matrix(m+2, m+2, r, c, M[r+1, c]); (P~*N~^-1)[n+2, 2]}
%Y A166906 Cf. A166905, A158831, A166907, A166908, A166909.
%K A166906 nonn
%O A166906 0,2
%A A166906 _Paul D. Hanna_, Nov 28 2009