%I #27 Feb 06 2022 15:01:21

%S 1,2,5,23,92,624,5021,47034,494320,5719769,71971687

%N Number of directed 2-regular graphs on n nodes.

%H 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 R. J. Mathar, <a href="/A219889/a219889.pdf">OEIS A219889</a>

%H 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 Column k=2 of A350910.

%Y 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 nonn,more

%O 3,2

%A _N. J. A. Sloane_, Nov 30 2012