OFFSET
0,4
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..50
EXAMPLE
The a(0) = 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}], {0, n}], Union@@#==Range[n]&]]], {n, 0, 5}]
PROG
(PARI) \\ G defined in A008406.
a(n)=my(A=O(x*x^n)); if(n==0, 1, polcoef((G(n, A)-G(n-1, A))/(1-x), n)) \\ Andrew Howroyd, Feb 19 2024
CROSSREFS
The labeled version is A369191.
KEYWORD
nonn
AUTHOR
Gus Wiseman, Feb 18 2024
EXTENSIONS
a(8) onwards from Andrew Howroyd, Feb 19 2024
STATUS
approved