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 A327424 Number of unlabeled, non-connected or empty antichains of nonempty subsets of {1..n}. 2
 1, 1, 2, 4, 10, 33, 234, 16579 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS An antichain is a set of nonempty sets, none of which is a subset of any other. A singleton is considered to be connected. LINKS EXAMPLE Non-isomorphic representatives of the a(0) = 1 through a(4) = 10 antichains:   {}  {}  {}         {}             {}           {{1},{2}}  {{1},{2}}      {{1},{2}}                      {{1},{2,3}}    {{1},{2,3}}                      {{1},{2},{3}}  {{1},{2},{3}}                                     {{1},{2,3,4}}                                     {{1,2},{3,4}}                                     {{1},{2},{3,4}}                                     {{1},{2},{3},{4}}                                     {{1},{2,4},{3,4}}                                     {{1},{2,3},{2,4},{3,4}} CROSSREFS Partial sums of the positive-index terms of A327426. The covering case is A327426. The labeled version is A327354. The labeled covering case is A120338. Unlabeled antichains that are either not connected or not covering are A327437. The case without empty antichains is A327808. Cf. A014466, A293606, A326704, A327062, A327355. Sequence in context: A173489 A089476 A323207 * A220028 A006397 A297197 Adjacent sequences:  A327421 A327422 A327423 * A327425 A327426 A327427 KEYWORD nonn,more AUTHOR Gus Wiseman, Sep 26 2019 STATUS approved

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Last modified August 4 13:49 EDT 2020. Contains 336201 sequences. (Running on oeis4.)