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Number of labeled digraphs where every node has indegree 0 or outdegree 0 and no isolated nodes.
10

%I #11 Apr 13 2017 14:27:38

%S 1,0,2,6,50,510,7682,161406,4747010,194342910,11084390402,

%T 881008805886,97779099906050,15178191426486270,3302331237256396802,

%U 1008694542117649154046,433286992912494943469570

%N Number of labeled digraphs where every node has indegree 0 or outdegree 0 and no isolated nodes.

%C Also labeled graphs with 2-colored nodes with no isolated nodes where black nodes are only connected to white nodes and vice versa.

%F a(n) = Sum_{k=0..n} (-1)^(n-k)*binomial(n, k)*A001831(k)

%F a(n) = Sum_{k=0..n} binomial(n, k)*(2^k-2)^(n-k). - _Vladeta Jovovic_, Apr 04 2003

%Y Cf. A001831 (binomial transform), A002031, A047863.

%K nonn

%O 0,3

%A _Christian G. Bower_, Dec 15 1999

%E Last 4 terms corrected by _Vladeta Jovovic_, Apr 04 2003