OFFSET
0,3
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..50
FORMULA
Sum of first n+1 terms of row n of A008406.
EXAMPLE
The a(1) = 1 through a(4) = 9 graph edge sets:
{} {} {} {}
{12} {12} {12}
{12-13} {12-13}
{12-13-23} {12-34}
{12-13-14}
{12-13-23}
{12-13-24}
{12-13-14-23}
{12-13-24-34}
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}]], Length[#]<=n&]]], {n, 0, 5}]
PROG
(PARI) a(n) = if(n<=1, n>=0, polcoef(G(n, O(x*x^n))/(1-x), n)) \\ G(n) defined in A008406. - Andrew Howroyd, Feb 20 2024
CROSSREFS
The labeled version is A369192.
KEYWORD
nonn
AUTHOR
Gus Wiseman, Feb 18 2024
STATUS
approved