A308161 Number of isomorphism classes of Eulerian oriented graphs with n vertices.

1, 1, 1, 2, 3, 7, 24, 200, 5479, 439517, 91097868, 48916220147, 68628518786683, 254305521019154638, 2512451288680194070842, 66741359152815902974086530, 4802230893555589082929258033462, 942013815025325986980154281918094498, 506666364226468633163453153303288094604018

Offset: 0

Author

Brendan McKay, May 15 2019

Keywords

• nonn
• hard

Comments

Loops and 2-cycles are not permitted. Eulerian means that each vertex has equal in-degree and out-degree.

Examples

			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.
		

Crossrefs

A058338 is the same allowing 2-cycles.

A308111 is the same allowing both loops and 2-cycles.

Cf. A007081 (labeled), A308239 (connected).

Extensions

Terms a(12) and beyond from Andrew Howroyd, Apr 10 2020