A129418 Number of isomorphism classes of 4-regular loopless multigraphs of order n.

1, 0, 1, 1, 4, 7, 24, 60, 240, 930, 4701, 26637, 178569, 1339529, 11187064, 101871881, 1002594996, 10574095327, 118850827173, 1417140114336, 17860018997346, 237160827107408, 3309078044759285, 48396906463199522, 740331404753448181, 11821525310570525197

Offset: 0

Author

Brendan McKay, Apr 15 2007

Keywords

• nonn

Comments

Initial terms computed using software at http://users.cecs.anu.edu.au/~bdm/nauty/

Also number of carbon allotropes satisfying the octet rule, excluding stereoisomers. - Natan Arie Consigli, Jun 06 2017

Crossrefs

Column k=4 of A333330.

Cf. A129417, A129429, A129416, A129420, A129422, A129424, A129426.

Programs

nauty

geng -d1 ${n} -q | multig -r4 -u # Natan Arie Consigli, Jun 06 2017

Formula

Euler transform of A129417. - Andrew Howroyd, Mar 14 2020

Extensions

a(0)-a(1) by Natan Arie Consigli, Jun 06 2017

a(18)-a(25) from Andrew Howroyd, Mar 17 2020