A053517 Number of connected directed 2-multigraphs on n nodes.

1, 5, 132, 22662, 29174514, 286151774704, 21712410740238954, 12980058344488389640470, 62082372574276838787463958455, 2405193558246444686967534052419452898, 762399004073792344564641131264446658930745417

Offset: 1

Author

Vladeta Jovovic, Jan 14 2000

Keywords

• easy
• nonn

Comments

A 2-multigraph is similar to an ordinary graph except there are 0, 1 or 2 edges between any two nodes (self-loops are not allowed).

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..40

Crossrefs

Cf. A053467.

Formula

Inverse Euler transform of A053467.

Extensions

a(11) from Andrew Howroyd, Nov 07 2019