%I A002786 M1522 N0596
%S A002786 1,2,5,19,132,3107,623615
%N A002786 Semigroups of order n with 1 idempotent, considered to be equivalent 
               when they are isomorphic or anti-isomorphic (by reversal of the operator).
%D A002786 H. Juergensen and P. Wick, Die Halbgruppen von Ordnungen <= 7, Semigroup 
               Forum, 14 (1977), 69-79.
%D A002786 R. J. Plemmons, There are 15973 semigroups of order 6, Math. Algor., 
               2 (1967), 2-17; 3 (1968), 23.
%D A002786 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A002786 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%H A002786 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               Semigroup.html">Link to a section of The World of Mathematics.</a>
%H A002786 <a href="Sindx_Se.html#semigroups">Index entries for sequences related 
               to semigroups</a>
%Y A002786 Column 1 of A058123.
%Y A002786 Sequence in context: A089126 A113346 A054926 this_sequence A039719 A014466 
               A108799
%Y A002786 Adjacent sequences: A002783 A002784 A002785 this_sequence A002787 A002788 
               A002789
%K A002786 nonn,nice,hard
%O A002786 1,2
%A A002786 N. J. A. Sloane (njas(AT)research.att.com).