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A055538 Number of asymmetric types of (3,n)-hypergraphs without isolated nodes, under action of symmetric group S_3; asymmetric n-covers of an unlabeled 3-set. 0
4, 20, 65, 170, 383, 779, 1470, 2611, 4418, 7182, 11283, 17213, 25601, 37230, 53074, 74327, 102434, 139133, 186501, 246988, 323479, 419344, 538492, 685438, 865376, 1084236, 1348777, 1666664, 2046551, 2498179, 3032482, 3661673, 4399374 (list; graph; refs; listen; history; text; internal format)
OFFSET

3,1

COMMENTS

Cover may include both empty sets and multiple occurrences of a subset.

LINKS

Table of n, a(n) for n=3..35.

FORMULA

G.f. : (1/(1-x)^8-3/(1-x)^4/(1-x^2)^2+2/(1-x)^2/(1-x^3)^2-3/(1-x)^4+3/(1-x)^2/(1-x^2)+6/(1-x)^2-6/(1-x))/6.

EXAMPLE

There are 4 asymmetric (3,3)-hypergraphs without isolated nodes: {{1,2},{1,2},{1,3}}, {{1},{1,2},{1,2,3}}, {{1},{1,2},{2,3}}, {{1},{2},{1,3}}.

CROSSREFS

Cf. A005745.

Sequence in context: A225260 A131479 A194094 * A302317 A319779 A287244

Adjacent sequences:  A055535 A055536 A055537 * A055539 A055540 A055541

KEYWORD

nonn

AUTHOR

Vladeta Jovovic, Jul 09 2000

EXTENSIONS

More terms from James A. Sellers, Jul 11 2000

STATUS

approved

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Last modified August 18 20:02 EDT 2019. Contains 326109 sequences. (Running on oeis4.)