OFFSET
0,5
COMMENTS
The axiom of choice says that, given any set of nonempty sets Y, it is possible to choose a set containing an element from each. The strict version requires this set to have the same cardinality as Y, meaning no element is chosen more than once.
In the connected case, these are just graphs with more than one cycle.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..50
FORMULA
EXAMPLE
Non-isomorphic representatives of the a(4) = 7 graphs:
{{1,2},{1,3},{1,4},{2,3},{2,4}}
{{1,2},{1,3},{1,4},{2,3},{2,4},{3,4}}
MATHEMATICA
Table[Length[Select[Subsets[Subsets[Range[n], {2}]], Select[Tuples[#], UnsameQ@@#&]=={}&]], {n, 0, 5}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Dec 07 2023
EXTENSIONS
Terms a(7) and beyond from Andrew Howroyd, Dec 30 2023
STATUS
approved