A326907 - OEIS

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.

2, 2, 6, 28, 330, 28960, 216562364, 5592326182940100

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OFFSET

0,1

COMMENTS

Differs from A108800 in having a(0) = 2 instead of 1.

LINKS

Table of n, a(n) for n=0..7.

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.

Cf. A001930, A102895, A108798, A193674, A193675, A326880, A326881, A326883, A326898, A326908.

Sequence in context: A214446 A179320 A004304 * A270487 A058250 A179929

Adjacent sequences: A326904 A326905 A326906 * A326908 A326909 A326910

KEYWORD

nonn,more

AUTHOR

Gus Wiseman, Aug 03 2019

EXTENSIONS

a(7) added from A108800 by Andrew Howroyd, Aug 10 2019

STATUS

approved