A049512 Number of quasi-initially connected digraphs on n unlabeled nodes.

1, 2, 13, 197, 9312, 1528634, 880277970

Offset

1,2

Comments

From Sean A. Irvine, Aug 01 2021: (Start)

A quasi-initially connected digraph is a digraph containing at least one vertex v such that every vertex u in the graph can either be reached from v or v can be reached from u (while obeying the directions on the edges).

There is no known formula. (End)

Links

Table of n, a(n) for n=1..7.

Sean A. Irvine, Java program (github)

V. Jovovic and G. Kilibarda, Enumeration of labeled quasi-initially connected digraphs, Discrete Math., 224 (2000), 151-163.

Crossrefs

Cf. A049414, A003085, A035512, A003088, A051421.

Sequence in context: A239994 A242007 A376550 * A003507 A338979 A307066

Adjacent sequences: A049509 A049510 A049511 * A049513 A049514 A049515

Keyword

hard,more,nonn

Author

Vladeta Jovovic, Goran Kilibarda

Extensions

a(6)-a(7) from Sean A. Irvine, Aug 01 2021

Status

approved