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A052332
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Number of labeled digraphs where every node has indegree 0 or outdegree 0 and no isolated nodes.
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7
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1, 0, 2, 6, 50, 510, 7682, 161406, 4747010, 194342910, 11084390402, 881008805886, 97779099906050, 15178191426486270, 3302331237256396802, 1008694542117649154046, 433286992912494943469570
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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COMMENTS
| Also labeled graphs with 2-colored nodes with no isolated nodes where black nodes are only connected to white nodes and vice versa.
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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 (vladeta(AT)eunet.rs), Apr 04 2003
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CROSSREFS
| Cf. A001831, A002031, A047863.
Sequence in context: A103990 A079835 A177454 * A134047 A078464 A108905
Adjacent sequences: A052329 A052330 A052331 * A052333 A052334 A052335
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KEYWORD
| nonn
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AUTHOR
| Christian G. Bower (bowerc(AT)usa.net), Dec 15 1999.
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EXTENSIONS
| Last 4 terms corrected by Vladeta Jovovic (vladeta(AT)eunet.rs), Apr 04 2003
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