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 A105616 #3 Mar 30 2012 18:36:45
%S A105616 1,4,26,226,2426,30826,451586,7489426,138722426,2839238026,
%T A105616 63654973826,1551919194226,40888965122426,1157981114051626,
%U A105616 35083865696279426,1132449247218851026,38800104353355372026,1406432065083818193226
%N A105616 Column 1 of triangle A105615.
%C A105616 Also equals column 0 of triangle A105623 (offset 1), where A105623 equals the matrix square-root of triangle A105615.
%o A105616 (PARI) {a(n)=if(n<0,0,(matrix(n+2,n+2,m,j,if(m>=j,if(m==j,1,if(m==j+1,-2*j, polcoeff(1/sum(i=0,m-j,(2*i)!/i!/2^i*x^i)+O(x^m),m-j) ))))^-1)[n+2,2])}
%Y A105616 Cf. A105615, A105623.
%K A105616 nonn
%O A105616 0,2
%A A105616 _Paul D. Hanna_, Apr 16 2005