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%I #35 Jul 25 2017 02:16:26
%S 1,1,3,22,485,59386,133059751,64649980092538
%N Number of different antimatroids on n labeled items.
%C 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.
%C 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
%H D. Eppstein, <a href="https://11011110.github.io/blog/2006/06/18/reverse-search-for.html">Reverse search for antimatroids</a>.
%H Yulia Kempner, Vadim E. Levit, <a href="http://arxiv.org/abs/math/0307013">Correspondence between two antimatroid algorithmic characterizations</a>, arXiv:math/0307013 [math.CO], 2003.
%H P. Uznanski <a href="http://paracombinatorics.wordpress.com/2013/04/19/enumeration-of-antimatroids-part-iv/">Enumeration of antimatroids</a>
%e 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}.
%Y Cf. A224913 (counts antimatroids, taking symmetries into account).
%K nonn,more
%O 0,3
%A _David Eppstein_, Jun 19 2006
%E Term for n=6 added based on a computer search by Przemysław Uznański - _David Eppstein_, Feb 26 2013
%E Term for n=7 added by _Przemyslaw Uznanski_, computed by Przemysław Uznański and Michał Bartoszkiewicz, Apr 19 2013