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A326883
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Number of unlabeled set-systems with {} that are closed under intersection and cover n vertices.
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9
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OFFSET
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0,3
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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) = 1 through a(3) = 22 set-systems:
{{}} {{}{1}} {{}{12}} {{}{123}}
{{}{1}{2}} {{}{1}{23}}
{{}{2}{12}} {{}{3}{123}}
{{}{1}{2}{12}} {{}{1}{2}{3}}
{{}{23}{123}}
{{}{1}{3}{23}}
{{}{2}{3}{123}}
{{}{3}{13}{23}}
{{}{1}{23}{123}}
{{}{3}{23}{123}}
{{}{1}{2}{3}{23}}
{{}{1}{2}{3}{123}}
{{}{2}{3}{13}{23}}
{{}{1}{3}{23}{123}}
{{}{2}{3}{23}{123}}
{{}{3}{13}{23}{123}}
{{}{1}{2}{3}{13}{23}}
{{}{1}{2}{3}{23}{123}}
{{}{2}{3}{13}{23}{123}}
{{}{1}{2}{3}{12}{13}{23}}
{{}{1}{2}{3}{13}{23}{123}}
{{}{1}{2}{3}{12}{13}{23}{123}}
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CROSSREFS
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The case also closed under union is A001930.
The connected case (i.e., with maximum) is A108798.
The same for union instead of intersection is (also) A108798.
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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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