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

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

Offset: 1

Author

Vladeta Jovovic, Goran Kilibarda

Keywords

• hard
• more
• nonn

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

• 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.

Extensions

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