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A319635
Number of non-isomorphic weight-n antichains of distinct multisets whose dual is also an antichain of (not necessarily distinct) multisets.
0
1, 1, 2, 3, 5, 7, 12, 16, 26, 36, 58
OFFSET
0,3
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}}.
The weight of a multiset partition is the sum of sizes of its parts. Weight is generally not the same as number of vertices.
EXAMPLE
Non-isomorphic representatives of the a(1) = 1 through a(5) = 7 antichains:
1: {{1}}
2: {{1,2}}
{{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},{3,4}}
{{1},{2},{3},{4}}
5: {{1,2,3,4,5}}
{{1},{2,3,4,5}}
{{1,2},{3,4,5}}
{{1},{2},{3,4,5}}
{{1},{2,3},{4,5}}
{{1},{2},{3},{4,5}}
{{1},{2},{3},{4},{5}}
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Sep 25 2018
STATUS
approved