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 A326944 Number of T_0 sets of subsets of {1..n} that cover all n vertices, contain {}, and are closed under intersection. 7
 1, 1, 4, 58, 3846, 2685550, 151873991914, 28175291154649937052 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS The dual of a multiset partition has, for each vertex, one block consisting of the indices (or positions) of the blocks containing that vertex. For example, the dual of {{1,2},{2,3}} is {{1},{1,2},{2}}. The T_0 condition means that the dual is strict (no repeated edges). LINKS FORMULA a(n) = Sum_{k=0..n} Stirling1(n,k)*A326881(k). - Andrew Howroyd, Aug 14 2019 EXAMPLE The a(0) = 1 through a(2) = 4 sets of subsets:   {{}}  {{},{1}}  {{},{1},{2}}                   {{},{1},{1,2}}                   {{},{2},{1,2}}                   {{},{1},{2},{1,2}} MATHEMATICA dual[eds_]:=Table[First/@Position[eds, x], {x, Union@@eds}]; Table[Length[Select[Subsets[Subsets[Range[n]]], MemberQ[#, {}]&&Union@@#==Range[n]&&UnsameQ@@dual[#]&&SubsetQ[#, Intersection@@@Tuples[#, 2]]&]], {n, 0, 3}] CROSSREFS The version not closed under intersection is A059201. The non-T_0 version is A326881. The version where {} is not necessarily an edge is A326943. Cf. A003181, A003465, A055621, A182507, A245567, A316978, A319564, A326906, A326939, A326941, A326945, A326947. Sequence in context: A295406 A229528 A109056 * A155204 A290765 A144992 Adjacent sequences:  A326941 A326942 A326943 * A326945 A326946 A326947 KEYWORD nonn,more AUTHOR Gus Wiseman, Aug 08 2019 EXTENSIONS a(5)-a(7) from Andrew Howroyd, Aug 14 2019 STATUS approved

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Last modified February 27 10:15 EST 2020. Contains 332304 sequences. (Running on oeis4.)