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A326883 Number of unlabeled set-systems with {} that are closed under intersection and cover n vertices. 9
1, 1, 4, 22, 302, 28630, 216533404, 5592325966377736 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,3
LINKS
FORMULA
a(n) = A108800(n) - A108800(n-1) for n > 0. - Andrew Howroyd, Aug 10 2019
EXAMPLE
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}}
CROSSREFS
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.
The non-covering case is A108800.
The labeled case is A326881.
Sequence in context: A265908 A359111 A119009 * A317803 A053722 A336212
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Jul 30 2019
EXTENSIONS
a(5)-a(7) from Andrew Howroyd, Aug 10 2019
STATUS
approved

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Last modified February 29 16:27 EST 2024. Contains 370425 sequences. (Running on oeis4.)