%I A003091 M1870
%S A003091 1,1,1,2,8,45,416,6657,189372,9695869,902597327,154043277297,48535481831642,
%T A003091 28400190511772276,31020581422991798557,63530150754287203445810,
%U A003091 244912468225468597942626507,1783398168624923337196441201196,24605638395579573858211783276124626
%N A003091 [ 2^{n(n-1)/2} / n! ].
%D A003091 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A003091 F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 
               1973, p. 246.
%p A003091 A003091:n->floor(2^(n*(n-1)/2)/n!);
%Y A003091 Sequence in context: A009345 A084553 A144164 this_sequence A119501 A006664 
               A141117
%Y A003091 Adjacent sequences: A003088 A003089 A003090 this_sequence A003092 A003093 
               A003094
%K A003091 nonn,easy
%O A003091 1,4
%A A003091 N. J. A. Sloane (njas(AT)research.att.com).