A289986 Number of connected 2n-regular loopless multigraphs on 2n unlabeled nodes.

1, 1, 3, 120, 543116, 635669057538, 112368754788708539549

Offset

0,3

Comments

Multigraphs are loopless.

There are no (2n+1)-regular multigraphs with (2n+1) number of points, for every nonnegative n.

Links

Table of n, a(n) for n=0..6.

Formula

a(n) = A328682(2*n, 2*n). - Andrew Howroyd, Mar 18 2020

Prog

(nauty/bash)  for n in {1..4}; do geng -c -d1 $[2*$n] -q | multig -m$[2*$n] -r$[2*$n] -u; done

Crossrefs

Cf. A005177, A129417, A129421, A129425, A328682.

Sequence in context: A289704 A246292 A202768 * A301559 A141440 A156001

Adjacent sequences: A289983 A289984 A289985 * A289987 A289988 A289989

Keyword

nonn,more,hard

Author

Natan Arie Consigli, Aug 19 2017

Extensions

a(5)-a(6) from Andrew Howroyd, Mar 18 2020

Status

approved