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Number of directed 2-regular graphs on n nodes without directed 2-cycles.
1

%I #12 Mar 12 2019 07:24:53

%S 1,4,9,55,453,4357,47598,569769,7371560,102525991,1525164223

%N Number of directed 2-regular graphs on n nodes without directed 2-cycles.

%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.

%Y Cf. A096368, A219889, A219890, A219891, A219892, A219893, A219895.

%K nonn,more

%O 5,2

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

%E a(14) and a(15) from _Brendan McKay_, Mar 12 2019