OFFSET
0,3
COMMENTS
A path is Hamiltonian if it passes through every vertex exactly once.
LINKS
Wikipedia, Hamiltonian path
Gus Wiseman, Enumeration of paths and cycles and e-coefficients of incomparability graphs, arXiv:0709.0430 [math.CO], 2007.
EXAMPLE
The a(2) = 12 edge-sets:
{12}
{21}
{11,12}
{11,21}
{12,21}
{12,22}
{21,22}
{11,12,21}
{11,12,22}
{11,21,22}
{12,21,22}
{11,12,21,22}
MATHEMATICA
Table[Length[Select[Subsets[Tuples[Range[n], 2]], FindHamiltonianPath[Graph[Range[n], DirectedEdge@@@#]]!={}&]], {n, 4}] (* Mathematica 10.2+ *)
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Jun 15 2019
STATUS
approved