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

1,2

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

Prog

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

Crossrefs

The labeled case is A003028.

Row sums of A057277.

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

Sequence in context: A039748 A007764 A015195 * A182162 A258994 A110105

Adjacent sequences: A051418 A051419 A051420 * A051422 A051423 A051424

Keyword

nonn,nice

Author

Vladeta Jovovic

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

Status

approved