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%I #19 Apr 10 2020 21:02:51
%S 1,1,1,2,3,7,24,200,5479,439517,91097868,48916220147,68628518786683,
%T 254305521019154638,2512451288680194070842,66741359152815902974086530,
%U 4802230893555589082929258033462,942013815025325986980154281918094498,506666364226468633163453153303288094604018
%N Number of isomorphism classes of Eulerian oriented graphs with n vertices.
%C Loops and 2-cycles are not permitted. Eulerian means that each vertex has equal in-degree and out-degree.
%e For n=4, the a(4)=3 solutions are an empty graph, a directed 3-cycle plus an isolated vertex, and a directed 4-cycle.
%Y A058338 is the same allowing 2-cycles.
%Y A308111 is the same allowing both loops and 2-cycles.
%Y Cf. A007081 (labeled), A308239 (connected).
%K nonn,hard
%O 0,4
%A _Brendan McKay_, May 15 2019
%E Terms a(12) and beyond from _Andrew Howroyd_, Apr 10 2020