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 A120945 #5 May 10 2013 12:45:46
%S A120945 1,2,1,8,18,12,1,18,108,272,300,120,1,33,393,2102,5700,8160,5880,1680,
%T A120945 1,54,1122,10688,53550,153132,258720,255360,136080,30240,1,82,2754,
%U A120945 42752,351650,1688892,5025832,9540272,11566800,8668800,3659040,665280
%N A120945 Triangle T(n,k) of number of labeled directed multigraphs (with loops), without isolated vertices, with n arrows and k vertices (n = 1,2,.., k = 1..2*n).
%F A120945 T(n,k) = Sum_{j=0..k} (-1)^(k-j)*binomial(k,j)*binomial(j^2+n-1,n). Row sums give A104209.
%F A120945 E.g.f.: exp(-x)*Sum((1-y)^(-n^2)*x^n/n!,n=0..infinity). - _Vladeta Jovovic_, Aug 24 2006
%e A120945 [1,2], [1,8,18,12], [1,18,108,272,300,120], [1,33,393,2102,5700,8160,5880,1680], ....
%Y A120945 Row sums give A104209.
%K A120945 nonn,tabf
%O A120945 1,2
%A A120945 _Vladeta Jovovic_, Aug 19 2006