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A319640 Number of non-isomorphic antichain covers of n vertices by distinct sets whose dual is also an antichain of distinct sets. 0
1, 1, 1, 2, 7, 70 (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
Non-isomorphic representatives of the a(1) = 1 through a(4) = 7 antichains:
1: {{1}}
2: {{1},{2}}
3: {{1},{2},{3}}
{{1,2},{1,3},{2,3}}
4: {{1},{2},{3},{4}}
{{1},{2,3},{2,4},{3,4}}
{{1,2},{1,3},{1,4},{2,3,4}}
{{1,2},{1,3},{2,4},{3,4}}
{{1,2,3},{1,2,4},{1,3,4},{2,3,4}}
{{1,3},{1,4},{2,3},{2,4},{3,4}}
{{1,2},{1,3},{1,4},{2,3},{2,4},{3,4}}
CROSSREFS
Sequence in context: A217069 A323673 A366359 * A260566 A113866 A165978
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Sep 25 2018
STATUS
approved

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Last modified March 28 04:58 EDT 2024. Contains 371235 sequences. (Running on oeis4.)