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A111637 Number of labeled graphs having n blue nodes and n green ones, where edges join only nodes of different colors. 1
1, 4, 96, 10240, 4587520, 8455716864, 63496796504064, 1932044240141942784, 237409596228641929297920, 117555946699326540948428554240, 234206054295766751302924897412448256, 1875359927045089548108556844295368069873664 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

a(n) = A111636(2n,n).

REFERENCES

H. S. Wilf, Generatingfunctionology, 2nd edn., Academic Press, NY, 1994, p. 88.

LINKS

Table of n, a(n) for n=0..11.

FORMULA

a(n) = C(2n,n)*2^(n^2).

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.

MAPLE

a:= n-> 2^(n^2)*binomial(2*n, n): seq(a(n), n=0..12);

CROSSREFS

Cf. A111636.

Sequence in context: A190196 A065140 A007106 * A027872 A308146 A203517

Adjacent sequences:  A111634 A111635 A111636 * A111638 A111639 A111640

KEYWORD

nonn

AUTHOR

Emeric Deutsch, Aug 09 2005

STATUS

approved

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Last modified April 14 09:23 EDT 2021. Contains 342948 sequences. (Running on oeis4.)