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 A107725 #3 Mar 30 2012 18:36:46
%S A107725 0,1,4,31,343,4855,83209,1670743,38436673,996825703,28778874481,
%T A107725 915636860023,31837734460129,1201360385000071,48899006799783889,
%U A107725 2135779996980897175,99646497213608842561,4946194601237466540967
%N A107725 Column 0 of A107724, which is the matrix logarithm of triangle A107719.
%o A107725 (PARI) {a(n)=local(L,M=matrix(n+1,n+1,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); L=sum(i=1,#M,(-1)^(i-1)*(M-M^0)^i/i);return(if(n<0,0,L[n+1,1]/3))}
%Y A107725 Cf. A107717, A107719, A107724.
%K A107725 nonn
%O A107725 0,3
%A A107725 _Paul D. Hanna_, May 30 2005