Search: id:A002787
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%I A002787 M1802 N0712
%S A002787 2,7,37,216,1780,32652
%N A002787 Number of semigroups of order n with 2 idempotents, considered to be 
               equivalent when they are isomorphic or anti-isomorphic (by reversal 
               of the operator).
%D A002787 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A002787 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A002787 H. Juergensen and P. Wick, Die Halbgruppen von Ordnungen <= 7, Semigroup 
               Forum, 14 (1977), 69-79.
%D A002787 R. J. Plemmons, There are 15973 semigroups of order 6, Math. Algor., 
               2 (1967), 2-17; 3 (1968), 23.
%H A002787 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 A002787 <a href="Sindx_Se.html#semigroups">Index entries for sequences related 
               to semigroups</a>
%Y A002787 Column 2 of A058123.
%Y A002787 Sequence in context: A042465 A041051 A047066 this_sequence A062394 A063766 
               A020040
%Y A002787 Adjacent sequences: A002784 A002785 A002786 this_sequence A002788 A002789 
               A002790
%K A002787 nonn
%O A002787 2,1
%A A002787 N. J. A. Sloane (njas(AT)research.att.com).

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