%I A003097 M2677
%S A003097 1,3,7,20,52,157
%N A003097 Critical connected topologies with n points.
%D A003097 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A003097 S. K. Das, On the enumeration of finite maximal connected topologies, 
               J. Combin. Theory, B 15 (1973), 184-199.
%Y A003097 Sequence in context: A111974 A066315 A058499 this_sequence A109220 A018034 
               A000227
%Y A003097 Adjacent sequences: A003094 A003095 A003096 this_sequence A003098 A003099 
               A003100
%K A003097 nonn
%O A003097 2,2
%A A003097 N. J. A. Sloane (njas(AT)research.att.com).