%I #17 Oct 19 2022 07:16:49
%S 1,4,21,232,14425,3653196,17705858989,261353065517776,
%T 241809117107232026097
%N Number of (open and closed) trails in the complete undirected graph on n labeled vertices.
%C Trails are directed and pass through each (undirected) edge at most once in either of the two directions.
%F a(n) = n * A357855(n) + n * (n-1) * A357856(n).
%Y Cf. A007082, A135388, A232545, A350028, A356366, A357855, A357856, A357885, A357886, A357887.
%K nonn,more,walk
%O 1,2
%A _Max Alekseyev_, Oct 16 2022
%E a(9) from _Bert Dobbelaere_, Oct 17 2022