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A129418
Number of isomorphism classes of 4-regular loopless multigraphs of order n.
8
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
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
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