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%I #44 Mar 18 2020 18:43:29
%S 1,1,3,120,543116,635669057538,112368754788708539549
%N Number of connected 2n-regular loopless multigraphs on 2n unlabeled nodes.
%C Multigraphs are loopless.
%C There are no (2n+1)-regular multigraphs with (2n+1) number of points, for every nonnegative n.
%F a(n) = A328682(2*n, 2*n). - _Andrew Howroyd_, Mar 18 2020
%o (nauty/bash) for n in {1..4}; do geng -c -d1 $[2*$n] -q | multig -m$[2*$n] -r$[2*$n] -u; done
%Y Cf. A005177, A129417, A129421, A129425, A328682.
%K nonn,more,hard
%O 0,3
%A _Natan Arie Consigli_, Aug 19 2017
%E a(5)-a(6) from _Andrew Howroyd_, Mar 18 2020
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