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 A326940 Number of T_0 set-systems on n vertices. 16
 1, 2, 7, 112, 32105, 2147161102, 9223372004645756887, 170141183460469231537996491362807709908, 57896044618658097711785492504343953921871039195927143534469727707459805807105 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 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, counted with multiplicity. 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 Table of n, a(n) for n=0..8. FORMULA Binomial transform of A059201. EXAMPLE The a(0) = 1 through a(2) = 7 set-systems: {} {} {} {{1}} {{1}} {{2}} {{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], {1, n}]], UnsameQ@@dual[#]&]], {n, 0, 3}] CROSSREFS The non-T_0 version is A058891 shifted to the left. The covering case is A059201. The version with empty edges is A326941. The unlabeled version is A326946. Cf. A003180, A316978, A319559, A319564, A319637, A326939, A326947, A326949. Sequence in context: A224445 A000157 A264999 * A326964 A034902 A101429 Adjacent sequences: A326937 A326938 A326939 * A326941 A326942 A326943 KEYWORD nonn AUTHOR Gus Wiseman, Aug 07 2019 STATUS approved

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Last modified November 28 09:18 EST 2023. Contains 367412 sequences. (Running on oeis4.)