OFFSET
0,4
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..500
FORMULA
EXAMPLE
Representatives of the a(2) = 1 through a(5) = 10 simple graphs:
{12} {12}{13} {12}{34} {12}{13}{45}
{12}{13}{23} {12}{13}{14} {12}{13}{14}{15}
{12}{13}{24} {12}{13}{14}{25}
{12}{13}{14}{23} {12}{13}{23}{45}
{12}{13}{24}{34} {12}{13}{24}{35}
{12}{13}{14}{15}{23}
{12}{13}{14}{23}{25}
{12}{13}{14}{23}{45}
{12}{13}{14}{25}{35}
{12}{13}{24}{35}{45}
MATHEMATICA
brute[m_]:=First[Sort[Table[Sort[Sort /@ (m/.Rule@@@Table[{(Union@@m)[[i]], p[[i]]}, {i, Length[p]}])], {p, Permutations[Range[Length[Union@@m]]]}]]];
Table[Length[Union[brute /@ Select[Subsets[Subsets[Range[n], {2}]], Union@@#==Range[n] && Length[Select[Tuples[#], UnsameQ@@#&]]!=0&]]], {n, 0, 5}]
CROSSREFS
The complement is counted by A369202.
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jan 23 2024
STATUS
approved