A051421 Number of digraphs on n unlabeled nodes with a sink (or, with a source).

1, 2, 12, 185, 8990, 1505939, 875542491, 1789247738400, 13018820342147705, 341188114831706152794, 32520852428719860881939391, 11366533535523591133597276823755, 14669006027884671703581740693080811331, 70315546525961698601351615055416574931833334

Offset: 1

Author

Vladeta Jovovic

Keywords

• nonn
• nice

Comments

Here a sink is defined to be a node to which all other nodes have a directed path. - Andrew Howroyd, Dec 27 2021

References

• F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 218 (incorrect version).
• Ronald C. Read, email to N. J. A. Sloane, 28 August, 2000.

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..50

Crossrefs

The labeled case is A003028.

Row sums of A057277.

Cf. A003085, A035512, A003088, A049531, A350415, A350360, A350794.

Programs

PARI

\\ See PARI link in A350794 for program code.
A051421seq(15) \\ Andrew Howroyd, Jan 21 2022

Extensions

a(6) corrected and a(7) from Sean A. Irvine, Sep 11 2021

a(0)=1 removed and terms a(8) and beyond from Andrew Howroyd, Jan 21 2022