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A108798 Number of nonisomorphic systems enumerated by A102894; that is, the number of inequivalent closure operators in which the empty set is closed. Also, the number of union-closed sets with n elements that contain the universe and the empty set. 8
1, 1, 3, 14, 165, 14480, 108281182, 2796163091470050 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

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

G. Brinkmann and R. Deklerck, Generation of Union-Closed Sets and Moore Families, Journal of Integer Sequences, Vol.21 (2018), Article 18.1.7.

G. Brinkmann and R. Deklerck, Generation of Union-Closed Sets and Moore Families, arXiv:1701.03751 [math.CO], 2017

CROSSREFS

Equals (1/2)*A108800(n).

Cf. A102894, A102895, A102897, A193674, A108800, A193675.

Sequence in context: A090897 A120459 A272368 * A260995 A220438 A250001

Adjacent sequences:  A108795 A108796 A108797 * A108799 A108800 A108801

KEYWORD

nonn,more,changed

AUTHOR

Don Knuth, Jul 01 2005

EXTENSIONS

a(6) added (using A193674) by N. J. A. Sloane, Aug 02 2011

Added a(7), and reference to union-closed sets. - Gunnar Brinkmann, Feb 05 2018

STATUS

approved

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Last modified February 23 21:23 EST 2018. Contains 299588 sequences. (Running on oeis4.)