OFFSET
0,7
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..200
FORMULA
EXAMPLE
The term a(6) = 90 counts all permutations of the (non-connected) graph {{1,2},{1,3},{1,4},{2,3},{2,4},{5,6}}.
MATHEMATICA
Table[Length[Select[Subsets[Subsets[Range[n], {2}], {n}], Union@@#==Range[n]&&Length[Select[Tuples[#], UnsameQ@@#&]]==0&]], {n, 0, 6}]
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jan 21 2024
EXTENSIONS
a(8) onwards from Andrew Howroyd, Feb 02 2024
STATUS
approved