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A108800
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Number of nonisomorphic systems enumerated by A102895.
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15
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OFFSET
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0,2
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COMMENTS
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Also the number of non-isomorphic sets of sets with {} that are closed under intersection. Also the number of non-isomorphic set-systems (without {}) covering n + 1 vertices and closed under intersection. - Gus Wiseman, Aug 05 2019
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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) = 28 sets of sets with {} that are closed under intersection:
{} {} {} {}
{}{1} {}{1} {}{1}
{}{12} {}{12}
{}{1}{2} {}{123}
{}{2}{12} {}{1}{2}
{}{1}{2}{12} {}{1}{23}
{}{2}{12}
{}{3}{123}
{}{1}{2}{3}
{}{23}{123}
{}{1}{2}{12}
{}{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}
(End)
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CROSSREFS
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Except a(0) = 1, first differences of A193675.
The connected case (i.e., with maximum) is A108798.
The same for union instead of intersection is (also) A108798.
The case also closed under union is A326898.
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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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