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A326907 Number of non-isomorphic sets of subsets of {1..n} that are closed under union and cover all n vertices. First differences of A193675. 5
2, 2, 6, 28, 330, 28960, 216562364, 5592326182940100 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,1
COMMENTS
Differs from A108800 in having a(0) = 2 instead of 1.
LINKS
EXAMPLE
Non-isomorphic representatives of the a(0) = 2 through a(3) = 28 sets of sets:
{} {{1}} {{12}} {{123}}
{{}} {{}{1}} {{}{12}} {{}{123}}
{{2}{12}} {{3}{123}}
{{}{2}{12}} {{23}{123}}
{{1}{2}{12}} {{}{3}{123}}
{{}{1}{2}{12}} {{}{23}{123}}
{{1}{23}{123}}
{{3}{23}{123}}
{{13}{23}{123}}
{{}{1}{23}{123}}
{{}{3}{23}{123}}
{{}{13}{23}{123}}
{{2}{3}{23}{123}}
{{2}{13}{23}{123}}
{{3}{13}{23}{123}}
{{12}{13}{23}{123}}
{{}{2}{3}{23}{123}}
{{}{2}{13}{23}{123}}
{{}{3}{13}{23}{123}}
{{}{12}{13}{23}{123}}
{{2}{3}{13}{23}{123}}
{{3}{12}{13}{23}{123}}
{{}{2}{3}{13}{23}{123}}
{{}{3}{12}{13}{23}{123}}
{{2}{3}{12}{13}{23}{123}}
{{}{2}{3}{12}{13}{23}{123}}
{{1}{2}{3}{12}{13}{23}{123}}
{{}{1}{2}{3}{12}{13}{23}{123}}
CROSSREFS
The case without empty sets is A108798.
The case with a single covering edge is A108800.
First differences of A193675.
The case also closed under intersection is A326898 for n > 0.
The labeled version is A326906.
The same for union instead of intersection is (also) A326907.
Sequence in context: A214446 A179320 A004304 * A270487 A058250 A179929
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Aug 03 2019
EXTENSIONS
a(7) added from A108800 by Andrew Howroyd, Aug 10 2019
STATUS
approved

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Last modified March 29 02:23 EDT 2024. Contains 371264 sequences. (Running on oeis4.)