OFFSET
0,3
COMMENTS
LINKS
M. Habib and L. Nourine, The number of Moore families on n = 6, Discrete Math., 294 (2005), 291-296.
FORMULA
a(n) = A326901(n) / 2 for n > 0. - Andrew Howroyd, Aug 10 2019
EXAMPLE
The a(1) = 1 through a(3) = 16 set-systems:
{{1}} {{1,2}} {{1,2,3}}
{{1},{1,2}} {{1},{1,2,3}}
{{2},{1,2}} {{2},{1,2,3}}
{{3},{1,2,3}}
{{1,2},{1,2,3}}
{{1,3},{1,2,3}}
{{2,3},{1,2,3}}
{{1},{1,2},{1,2,3}}
{{1},{1,3},{1,2,3}}
{{2},{1,2},{1,2,3}}
{{2},{2,3},{1,2,3}}
{{3},{1,3},{1,2,3}}
{{3},{2,3},{1,2,3}}
{{1},{1,2},{1,3},{1,2,3}}
{{2},{1,2},{2,3},{1,2,3}}
{{3},{1,3},{2,3},{1,2,3}}
MATHEMATICA
Table[Length[Select[Subsets[Subsets[Range[n], {1, n}]], MemberQ[#, Range[n]]&&SubsetQ[#, Intersection@@@Tuples[#, 2]]&]], {n, 0, 3}]
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Aug 04 2019
EXTENSIONS
a(5)-a(8) from Andrew Howroyd, Aug 10 2019
STATUS
approved