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 A326942 Number of unlabeled T_0 sets of subsets of {1..n} that cover all n vertices. 5
 2, 2, 6, 58, 3770 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 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 FORMULA a(n) = 2 * A319637(n). EXAMPLE Non-isomorphic representatives of the a(0) = 2 through a(2) = 6 sets of subsets:   {}    {{1}}     {{1},{2}}   {{}}  {{},{1}}  {{2},{1,2}}                   {{},{1},{2}}                   {{},{2},{1,2}}                   {{1},{2},{1,2}}                   {{},{1},{2},{1,2}} CROSSREFS The non-T_0 version is A003181. The case without empty edges is A319637. The labeled version is A326939. The non-covering version is A326949 (partial sums). Cf. A000371, A003180, A055621, A059201, A316978, A319559, A319564, A326907, A326941, A326943, A326946. Sequence in context: A137244 A284707 A174589 * A247943 A329571 A270358 Adjacent sequences:  A326939 A326940 A326941 * A326943 A326944 A326945 KEYWORD nonn,more AUTHOR Gus Wiseman, Aug 07 2019 STATUS approved

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Last modified April 10 02:39 EDT 2020. Contains 333392 sequences. (Running on oeis4.)