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

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

Offset: 0

Author

Natan Arie Consigli, Aug 19 2017

Keywords

• nonn
• more
• hard

Comments

Multigraphs are loopless.

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

Crossrefs

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

Programs

nauty

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

Formula

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

Extensions

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