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A319639
Number of antichain covers of n vertices by distinct sets whose dual is also an antichain of distinct sets.
10
1, 1, 1, 2, 20, 2043
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}}.
EXAMPLE
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}}
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Sep 25 2018
STATUS
approved