A121936 Number of digraphs with labeled vertices and labeled arcs, with n arcs and with no vertex of indegree 0 or outdegree 0.
1, 0, 2, 18, 518, 23610, 1600982, 150451098, 18694217558, 2966151496410, 584994048653462, 140357794553191578, 40253455215544778198, 13598018000464234802010, 5343837921922909297592342
Offset: 0
Formula
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).
Extensions
More terms from Max Alekseyev, Jul 29 2009