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Search: id:A097629
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A097629 2*(2n)^(n-2). +0
5
1, 2, 12, 128, 2000, 41472, 1075648, 33554432, 1224440064, 51200000000, 2414538435584, 126806761930752, 7340688973975552, 464436530178424832, 31886460000000000000, 2361183241434822606848, 187591757103747287810048 (list; graph; listen)
OFFSET

1,2

COMMENT

Number of all unrooted directed trees on n nodes.

Ditrees are well-colored directed trees. Well-colored means, each green vertex has at least a red child, each red vertex has no red child.

LINKS

C. Banderier, J.-M. Le Bars and V. Ravelomanana, Generating functions for kernels of digraphs

FORMULA

E.g.f.: A(x) = B(x)-B(x)^2, B(x) = e.g.f. of A052746 or A(x) = C(2x)/2, C(x) = e.g.f. of A000272.

CROSSREFS

Equals (1/2) A038058 = A097630(n) + A097631(n). Cf. A052746, A097627.

Sequence in context: A035351 A003712 A143136 this_sequence A014235 A098628 A123553

Adjacent sequences: A097626 A097627 A097628 this_sequence A097630 A097631 A097632

KEYWORD

nonn

AUTHOR

Ralf Stephan, Aug 17 2004

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Last modified December 9 18:50 EST 2009. Contains 170568 sequences.


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