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A326949
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Number of unlabeled T_0 sets of subsets of {1..n}.
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7
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OFFSET
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0,1
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COMMENTS
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The dual of a set-system has, for each vertex, one edge consisting of the indices (or positions) of the edges containing that vertex. 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) = 10 sets of sets:
{} {} {}
{{}} {{}} {{}}
{{1}} {{1}}
{{},{1}} {{},{1}}
{{1},{2}}
{{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 covering case is A326942 (first differences).
The case without empty edges is A326946.
Cf. A000371, A000612, A003181, A059052, A245567, A316978, A319559, A319564, A319637, A326939, A326940.
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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