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 A219889 #27 Feb 06 2022 15:01:21 %S A219889 1,2,5,23,92,624,5021,47034,494320,5719769,71971687 %N A219889 Number of directed 2-regular graphs on n nodes. %H A219889 Gunnar Brinkmann, <a href="https://doi.org/10.1016/j.disc.2012.09.014">Generating regular directed graphs</a>, Discrete Math., 313 (2012), 1-7. %H A219889 R. J. Mathar, <a href="/A219889/a219889.pdf">OEIS A219889</a> %H A219889 Richard J. Mathar, <a href="https://arxiv.org/abs/1903.12477">2-regular Digraphs of the Lovelock Lagrangian</a>, arXiv:1903.12477 [math.GM], 2019. %Y A219889 Column k=2 of A350910. %Y A219889 Cf. A096368, A219890, A219891, A219892, A219893, A307155 (connected, inverse Euler Trans.), A007107 (labeled), A306827 (multiedges, connected), A002865 (directed 1-regular unlabeled no loops), A005641 (loops allowed) %K A219889 nonn,more %O A219889 3,2 %A A219889 _N. J. A. Sloane_, Nov 30 2012