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 A158838 #2 Mar 30 2012 18:37:16
%S A158838 1,3,21,217,2904,47337,906557,19910808,492818850,13564326950,
%T A158838 410807572044,13573135469214,485765085176420,18717987193565613,
%U A158838 772565258231236269,34002334709760133807,1589555183231724515700
%N A158838 Column 2 of triangle A158835.
%C A158838 Triangle A158835 transforms diagonals in the array A158825 of coefficients of successive iterations of x*C(x) where C(x) is the Catalan function (A000108).
%o A158838 (PARI) {a(n)=local(F=x, CAT=serreverse(x-x^2+x*O(x^(n+4))),M,N,P);M=matrix(n+4, n+4, r, c, F=x; for(i=1, r+c-2, F=subst(F, x, CAT)); polcoeff(F, c)); N=matrix(n+3, n+3, r, c, M[r, c]); P=matrix(n+3, n+3, r, c, M[r+1, c]); (P~*N~^-1)[n+3,3]}
%Y A158838 Cf. A158835, A158836, A158837, A158839, A158840.
%K A158838 nonn
%O A158838 0,2
%A A158838 _Paul D. Hanna_, Mar 28 2009