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

0,5

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

Links

Table of n, a(n) for n=0..25.

Formula

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

Prog

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

Crossrefs

Column k=4 of A333330.

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

Sequence in context: A203230 A143608 A079441 * A372169 A073218 A276288

Adjacent sequences: A129415 A129416 A129417 * A129419 A129420 A129421

Keyword

nonn

Author

Brendan McKay, Apr 15 2007

Extensions

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

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

Status

approved