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%I #34 Feb 23 2018 07:41:20
%S 0,0,0,2,27,3133,5777931
%N The number of sparse union-closed sets. That is, the number of union-closed sets on n elements containing the empty set and the universe, such that in average each set (not counting the empty set) has at most n/2 elements.
%C If there is a counterexample to the union-closed set conjecture, it is a sparse union-closed set.
%H G. Brinkmann and R. Deklerck, <a href="https://arxiv.org/abs/1701.03751"> Generation of Union-Closed Sets and Moore Families</a>, arXiv:1701.03751 [math.CO], 2017.
%H G. Brinkmann and R. Deklerck, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL21/Brinkmann/brink6.html"> Generation of Union-Closed Sets and Moore Families</a>, Journal of Integer Sequences, Vol.21 (2018), Article 18.1.7.
%Y Cf. A108798, A102894, A193674, A102896.
%K nonn,more
%O 1,4
%A _Gunnar Brinkmann_, Feb 05 2018
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