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A111637
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Number of labeled graphs having n blue nodes and n green ones, where edges join only nodes of different colors.
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1
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1, 4, 96, 10240, 4587520, 8455716864, 63496796504064, 1932044240141942784, 237409596228641929297920, 117555946699326540948428554240, 234206054295766751302924897412448256
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| a(n)=A111636(2n,n).
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REFERENCES
| H. S. Wilf, Generatingfunctionology, 2nd edn., Academic Press, NY, 1994, p. 88.
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FORMULA
| a(n)=C(2n, n)*2^(n^2).
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EXAMPLE
| a(1)=4 because we have B G, B--G, G B and G--B, where B (G) stands for a blue (green) node and -- denotes an edge.
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MAPLE
| a:=n->2^(n^2)*binomial(2*n, n): seq(a(n), n=0..12);
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CROSSREFS
| Cf. A111636.
Sequence in context: A190196 A065140 A007106 * A027872 A203517 A146514
Adjacent sequences: A111634 A111635 A111636 * A111638 A111639 A111640
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KEYWORD
| nonn
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AUTHOR
| Emeric Deutsch (deutsch(AT)duke.poly.edu), Aug 09 2005
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