1,2

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.

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

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.

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

nonn

Ralf Stephan, Aug 17 2004