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 A121936 #5 May 10 2013 12:45:47 %S A121936 1,0,2,18,518,23610,1600982,150451098,18694217558,2966151496410, %T A121936 584994048653462,140357794553191578,40253455215544778198, %U A121936 13598018000464234802010,5343837921922909297592342 %N A121936 Number of digraphs with labeled vertices and labeled arcs, with n arcs and with no vertex of indegree 0 or outdegree 0. %F A121936 E.g.f.: Sum(Sum((-1)^(n-k)*binomial(n,k)*(exp((k-1)*x)-1)^k*(exp(k*x)-1)^(n-k),k=0..n),n=0..infinity). %Y A121936 Cf. A122399, A122418. %K A121936 easy,nonn %O A121936 0,3 %A A121936 _Vladeta Jovovic_, Sep 03 2006 %E A121936 More terms from _Max Alekseyev_, Jul 29 2009