A052332 Number of labeled digraphs where every node has indegree 0 or outdegree 0 and no isolated nodes.

1, 0, 2, 6, 50, 510, 7682, 161406, 4747010, 194342910, 11084390402, 881008805886, 97779099906050, 15178191426486270, 3302331237256396802, 1008694542117649154046, 433286992912494943469570

Offset: 0

Author

Christian G. Bower, Dec 15 1999

Keywords

• nonn

Comments

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

Crossrefs

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

Formula

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

a(n) = Sum_{k=0..n} binomial(n, k)*(2^k-2)^(n-k). - Vladeta Jovovic, Apr 04 2003

Extensions

Last 4 terms corrected by Vladeta Jovovic, Apr 04 2003