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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: A271850 A364844 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 August 4 06:59 EDT 2024. Contains 374905 sequences. (Running on oeis4.)