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 A107718 #3 Mar 30 2012 18:36:46
%S A107718 1,6,57,723,11361,212151,4584081,112480887,3090105921,93988998183,
%T A107718 3136338148017,113945190405303,4477940877230625,189296643095867847,
%U A107718 8565988634172222609,413169192012610306263,21161884092470464784385
%N A107718 Column 1 of triangle A107717.
%C A107718 Equals one-half of column 0 of A107719 shift 1 place left.
%o A107718 (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,-3*j, polcoeff(1/sum(i=0,m-j,prod(r=0,i-1,3*r+1)*x^i)+O(x^m),m-j)))))^-1)[n+2,2])}
%Y A107718 Cf. A107717, A107719.
%K A107718 nonn
%O A107718 0,2
%A A107718 _Paul D. Hanna_, May 30 2005