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A289986
Number of connected 2n-regular loopless multigraphs on 2n unlabeled nodes.
4
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.
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
KEYWORD
nonn,more,hard
AUTHOR
Natan Arie Consigli, Aug 19 2017
EXTENSIONS
a(5)-a(6) from Andrew Howroyd, Mar 18 2020
STATUS
approved