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A320446
Covers of triangles by tetrahedra: number of labeled 4-uniform hypergraphs spanning n vertices such that every three vertices appear together in some edge.
0
1, 1, 1, 0, 1, 6, 5789
OFFSET
0,6
EXAMPLE
The a(5) = 6 hypergraphs:
{{1234},{1235},{1245},{1345}}
{{1234},{1235},{1245},{2345}}
{{1234},{1235},{1345},{2345}}
{{1234},{1245},{1345},{2345}}
{{1235},{1245},{1345},{2345}}
{{1234},{1235},{1245},{1345},{2345}}
MATHEMATICA
Table[Length[Select[Subsets[Subsets[Range[n], {4}]], Length[Union@@(Subsets[#, {3}]&/@#)]==Binomial[n, 3]&]], {n, 6}]
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Jan 10 2019
STATUS
approved