

A308111


Isomorphism classes of Eulerian digraphs with n vertices, allowing loops.


5



1, 2, 6, 24, 160, 2512, 129816, 22665792, 13056562208, 24953006054144, 160860329639968800, 3555065836569542246400, 273147301191314006316868352, 73832333258502021627712839197696, 70920540648597652305602460997787710080, 244186544390677638132290202415190606165938176, 3036252267734950687777830287721323374283100639476736
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OFFSET

0,2


COMMENTS

Eulerian means that for every vertex the indegree equals the outdegree.


LINKS



FORMULA



EXAMPLE

For n=2 the a(2)=6 solutions are: two nonadjacent vertices with or without loops (3 cases), two vertices with or without loops connected by edges in each direction (3 cases).


CROSSREFS

For labeled digraphs rather than isomorphism classes see A229865.
For isomorphism classes with loops forbidden see A058338.
Cf. A308128 (connected version of this).


KEYWORD

nonn,hard


AUTHOR



EXTENSIONS



STATUS

approved



