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 A306892 #27 Mar 21 2023 05:24:27 %S A306892 1,1,2,5,14,50,265,1601,11984,101884 %N A306892 Isomorphism classes of connected 2-regular digraphs on n nodes, allowing multiarcs and loops. %C A306892 The graphs are directed, connected and have indegree=outdegree=2 at each node. Multiarcs (connecting two nodes with the same sense of heading) and loops (edges connecting a node to itself) are permitted. %C A306892 The sequence of the same family of graphs which are not necessarily connected is A006372 (the Euler transform of this sequence). %H A306892 R. J. Mathar, <a href="/A306892/a306892.pdf">OEIS A306892</a> %H A306892 R. J. Mathar, <a href="https://arxiv.org/abs/1903.12477">2-regular digraphs of the Lovelock Lagrangian</a>, arXiv:1903.12477 [math.GM] (2019). %e A306892 On n=1 node, the graph is the node with two edges looping back to the node. %e A306892 On n=2 nodes, the graph is either having two pairs of edges (4 edges in total) linking one node to the other, or a loop at each node and two edges (different senses) from one node to the other. %Y A306892 Cf. A306827 (no loops). %K A306892 nonn,more %O A306892 0,3 %A A306892 _R. J. Mathar_, Mar 15 2019 %E A306892 a(8) added by _R. J. Mathar_, Apr 08 2019 %E A306892 a(9) added by _R. J. Mathar_, Apr 15 2019