This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A289986 #47 Jun 02 2025 17:12:44
%S A289986 1,1,3,120,543116,635669057538,112368754788708539549
%N A289986 Number of connected 2n-regular loopless multigraphs on 2n unlabeled nodes.
%C A289986 Multigraphs are loopless.
%C A289986 There are no (2n+1)-regular multigraphs with (2n+1) number of points, for every nonnegative n.
%F A289986 a(n) = A328682(2*n, 2*n). - _Andrew Howroyd_, Mar 18 2020
%o A289986 (nauty) for n in {1..4}; do geng -c -d1 $[2*$n] -q | multig -m$[2*$n] -r$[2*$n] -u; done
%Y A289986 Cf. A005177, A129417, A129421, A129425, A328682.
%K A289986 nonn,more,hard
%O A289986 0,3
%A A289986 _Natan Arie Consigli_, Aug 19 2017
%E A289986 a(5)-a(6) from _Andrew Howroyd_, Mar 18 2020