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A119770 Number of different antimatroids on n labeled items. 1
1, 1, 3, 22, 485, 59386, 133059751, 64649980092538 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

See link for software to generate the sequence. The next item (for n=8) should be roughly 2^78 and seems hopeless without more mathematics.

Antimatroids are a subset of greedoids, usually defined either in terms of set systems, as David Eppstein does in his tree searches, or in terms of formal languages. The two are equivalent, as discussed in Kempner and Levit. - Jonathan Vos Post, Jun 20 2006

LINKS

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

D. Eppstein, Reverse search for antimatroids.

Yulia Kempner, Vadim E. Levit, Correspondence between two antimatroid algorithmic characterizations, arXiv:math/0307013 [math.CO], 2003.

P. Uznanski Enumeration of antimatroids

EXAMPLE

The three antimatroids on the two items 0 and 1 are (a) {},{0},{0,1}, (b) {},{1},{0,1} and (c) {},{0},{1},{0,1}.

CROSSREFS

Cf. A224913 (counts antimatroids, taking symmetries into account).

Sequence in context: A271849 A271850 A156512 * A272659 A233748 A153230

Adjacent sequences:  A119767 A119768 A119769 * A119771 A119772 A119773

KEYWORD

nonn,more

AUTHOR

David Eppstein, Jun 19 2006

EXTENSIONS

Term for n=6 added based on a computer search by Przemysław Uznański - David Eppstein, Feb 26 2013

Term for n=7 added by Przemyslaw Uznanski, computed by Przemysław Uznański and Michał Bartoszkiewicz, Apr 19 2013

STATUS

approved

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Last modified December 11 15:30 EST 2018. Contains 318049 sequences. (Running on oeis4.)