OFFSET
0,2
COMMENTS
Eulerian means that for every vertex the in-degree equals the out-degree.
LINKS
FORMULA
Euler transform of A308128.
EXAMPLE
For n=2 the a(2)=6 solutions are: two non-adjacent vertices with or without loops (3 cases), two vertices with or without loops connected by edges in each direction (3 cases).
CROSSREFS
KEYWORD
nonn,hard
AUTHOR
Brendan McKay, May 11 2019
EXTENSIONS
Terms a(10) and beyond from Andrew Howroyd, Apr 12 2020
STATUS
approved