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 A319620 Number of connected antichain covers of n vertices by distinct sets whose dual is also a (not necessarily strict) antichain. 0
 1, 1, 1, 2, 22, 2133 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 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},{2,2}} is {{1},{1,2,2}}. LINKS EXAMPLE The a(4) = 22 antichain covers:    {{1,2,3,4}}    {{3,4},{1,2,3},{1,2,4}}    {{2,4},{1,2,3},{1,3,4}}    {{2,3},{1,2,4},{1,3,4}}    {{1,4},{1,2,3},{2,3,4}}    {{1,3},{1,2,4},{2,3,4}}    {{1,2},{1,3,4},{2,3,4}}    {{1,3},{1,4},{2,3},{2,4}}    {{1,2},{1,4},{2,3},{3,4}}    {{1,2},{1,3},{2,4},{3,4}}    {{1,4},{2,4},{3,4},{1,2,3}}    {{1,3},{2,3},{3,4},{1,2,4}}    {{1,2},{2,3},{2,4},{1,3,4}}    {{1,2},{1,3},{1,4},{2,3,4}}    {{1,3},{1,4},{2,3},{2,4},{3,4}}    {{1,2},{1,4},{2,3},{2,4},{3,4}}    {{1,2},{1,3},{2,3},{2,4},{3,4}}    {{1,2},{1,3},{1,4},{2,4},{3,4}}    {{1,2},{1,3},{1,4},{2,3},{3,4}}    {{1,2},{1,3},{1,4},{2,3},{2,4}}    {{1,2,3},{1,2,4},{1,3,4},{2,3,4}}    {{1,2},{1,3},{1,4},{2,3},{2,4},{3,4}} CROSSREFS Cf. A006126, A007716, A007718, A049311, A056156, A059201, A283877, A316980, A316983, A318099, A319557, A319565, A319616-A319646, A300913. Sequence in context: A330124 A104149 A113761 * A054349 A182293 A222000 Adjacent sequences:  A319617 A319618 A319619 * A319621 A319622 A319623 KEYWORD nonn,more AUTHOR Gus Wiseman, Sep 25 2018 STATUS approved

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Last modified May 12 07:28 EDT 2021. Contains 343821 sequences. (Running on oeis4.)