A335601 The number of mixed trees with n nodes and n-2 arcs.

1, 2, 10, 40, 187, 854, 4074, 19602, 96035, 475492, 2380042, 12015368, 61130186, 313081232, 1612967974, 8353387992, 43464071199, 227101948596, 1191127734498, 6268882232536, 33096647906860, 175236408484988, 930271133498794, 4950509216635406, 26403755607304762, 141119182968584618

Offset

2,2

Comments

Mixed trees are trees where a subset of the edges are directed (edges called arcs then). This is the first subdiagonal of A335362: n nodes implies trees with n-1 edges. If exactly one of these edges is not directed and the remaining n-2 edges are directed, the trees are counted here.

Links

Table of n, a(n) for n=2..27.

Index entries for sequences related to trees

Formula

O.g.f. ( B(x)^2+B(x^2) )/2 where B(x) is the o.g.f. of A000151.

a(n) = A335362(n,n-2).

Crossrefs

Cf. A335362.

Sequence in context: A151025 A333799 A030534 * A151026 A151027 A188325

Adjacent sequences: A335598 A335599 A335600 * A335602 A335603 A335604

Keyword

nonn

Author

R. J. Mathar, Jun 15 2020

Status

approved