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A326942
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Number of unlabeled T_0 sets of subsets of {1..n} that cover all n vertices.
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5
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OFFSET
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0,1
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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},{2,3}} is {{1},{1,2},{2}}. The T_0 condition means that the dual is strict (no repeated edges).
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LINKS
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FORMULA
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EXAMPLE
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Non-isomorphic representatives of the a(0) = 2 through a(2) = 6 sets of subsets:
{} {{1}} {{1},{2}}
{{}} {{},{1}} {{2},{1,2}}
{{},{1},{2}}
{{},{2},{1,2}}
{{1},{2},{1,2}}
{{},{1},{2},{1,2}}
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CROSSREFS
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The case without empty edges is A319637.
The non-covering version is A326949 (partial sums).
Cf. A000371, A003180, A055621, A059201, A316978, A319559, A319564, A326907, A326941, A326943, A326946.
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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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