OFFSET
0,4
COMMENTS
Loops and 2-cycles are not permitted. Eulerian means that each vertex has equal in-degree and out-degree.
EXAMPLE
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
KEYWORD
nonn,hard
AUTHOR
Brendan McKay, May 15 2019
EXTENSIONS
Terms a(12) and beyond from Andrew Howroyd, Apr 10 2020
STATUS
approved