%I A137813
%S A137813 0,1,2,2,3,3,4,3,4,4,5,4,5,5,5,4,5,5,6,5,6,6,6,5,6,6,6,6,7,6,7,5,6,6,7,
%T A137813 6,7,7,7,6,7,7,7,7,7,7,8,6,7,7,7,7,8,7,8,7,8,8,8,7,8,8,8,6,7,7,8,7,8,8,
%U A137813 8,7,8,8,8,8,8,8,9,7,8,8,8,8,8,8,9,8,9,8,9,8,9,9,9,7,8,8,8,8,9,8,9,8,9
%N A137813 Minimal number of points needed to make a topology having k open sets.
%D A137813 K. Ragnarsson and B. E. Tenner, Obtainable sizes of topologies on finite 
               sets, preprint.
%e A137813 A topology having 7 open sets can be made on 4 points. The open sets 
               are: {}, {1}, {2}, {1,2}, {1,3}, {1,2,3}, {1,2,3,4}. No topology 
               having 7 open sets can be made with fewer points.
%Y A137813 Cf. A137814.
%Y A137813 Sequence in context: A139141 A122953 A128998 this_sequence A003313 A117497 
               A117498
%Y A137813 Adjacent sequences: A137810 A137811 A137812 this_sequence A137814 A137815 
               A137816
%K A137813 nonn
%O A137813 1,3
%A A137813 Bridget Eileen Tenner (bridget(AT)math.depaul.edu), Feb 11 2008