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A319639
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Number of antichain covers of n vertices by distinct sets whose dual is also an antichain of distinct sets.
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10
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OFFSET
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0,4
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COMMENTS
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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}}.
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LINKS
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EXAMPLE
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The a(1) = 1 through a(3) = 2 antichain covers:
1: {{1}}
2: {{1},{2}}
3: {{1},{2},{3}}
{{1,2},{1,3},{2,3}}
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CROSSREFS
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Cf. A006126, A007716, A049311, A059201, A283877, A293606, A316980, A316983, A318099, A319558, A319616-A319646, A300913.
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KEYWORD
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nonn,more
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AUTHOR
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STATUS
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approved
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