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 A326902 Number of set-systems (without {}) covering n vertices that are closed under intersection. 4
 1, 1, 3, 19, 319, 21881, 16417973, 1063459099837, 225402359008808647339 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS A set-system is a finite set of finite nonempty sets, so no two edges of a set-system that is closed under intersection can be disjoint. LINKS FORMULA Inverse binomial transform of A326901. - Andrew Howroyd, Aug 10 2019 EXAMPLE The a(0) = 1 through a(3) = 19 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},{1,3}}                           {{2},{1,2},{2,3}}                           {{3},{1,3},{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}]], Union@@#==Range[n]&&SubsetQ[#, Intersection@@@Tuples[#, 2]]&]], {n, 0, 3}] CROSSREFS The case closed under union and intersection is A006058. The case with union instead of intersection is A102894. The unlabeled version is A108800(n - 1). The non-covering case is A326901. The connected case is A326903. Cf. A000798, A001930, A102895, A102898, A182507, A326866, A326876, A326878, A326882, A326900, A326901, A326904. Sequence in context: A115705 A136171 A102586 * A346840 A132876 A229832 Adjacent sequences:  A326899 A326900 A326901 * A326903 A326904 A326905 KEYWORD nonn,more AUTHOR Gus Wiseman, Aug 04 2019 EXTENSIONS a(5)-a(8) from Andrew Howroyd, Aug 10 2019 STATUS approved

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Last modified September 16 23:53 EDT 2021. Contains 347477 sequences. (Running on oeis4.)