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A327355
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Number of antichains of nonempty subsets of {1..n} that are either non-connected or non-covering (spanning edge-connectivity 0).
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8
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OFFSET
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0,3
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COMMENTS
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An antichain is a set of sets, none of which is a subset of any other. It is covering if there are no isolated vertices.
The spanning edge-connectivity of a set-system is the minimum number of edges that must be removed (without removing incident vertices) to obtain a set-system that is disconnected or covers fewer vertices.
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LINKS
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FORMULA
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EXAMPLE
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The a(1) = 1 through a(3) = 14 antichains:
{} {} {}
{{1}} {{1}}
{{2}} {{2}}
{{1},{2}} {{3}}
{{1,2}}
{{1,3}}
{{2,3}}
{{1},{2}}
{{1},{3}}
{{2},{3}}
{{1},{2,3}}
{{2},{1,3}}
{{3},{1,2}}
{{1},{2},{3}}
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CROSSREFS
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The non-spanning edge-connectivity version is A327354.
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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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