%I A001426 M2929 N1177
%S A001426 1,1,3,12,58,325,2143,17291,221805,11545843,3518930337
%N A001426 Number of commutative semigroups of order n.
%D A001426 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A001426 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A001426 Grillet, P.A., Computing Finite Commutative Semigroups, Semigroup Forum 
               53 (1996), 140-154.
%D A001426 Grillet, P.A., Computing Finite Commutative Semigroups: Part II, Semigroup 
               Forum 67 (2003), 159-184.
%D A001426 H. Juergensen and P. Wick, Die Halbgruppen von Ordnungen <= 7, Semigroup 
               Forum, 14 (1977), 69-79.
%D A001426 R. J. Plemmons, There are 15973 semigroups of order 6, Math. Algor., 
               2 (1967), 2-17; 3 (1968), 23.
%D A001426 R. J. Plemmons, Cayley Tables for All Semigroups of Order Less Than 7. 
               Department of Mathematics, Auburn Univ., 1965.
%D A001426 Satoh, S.; Yama, K.; and Tokizawa, M., Semigroups of order 8, Semigroup 
               Forum 49 (1994), 7-29.
%H A001426 Eric Postpischil <a href="http://groups.google.com/groups?&hl=en&lr=&ie=UTF-8&selm=11802%40shlump.nac.dec.com\
               &rnum=2">Posting to sci.math newsgroup, May 21 1990</a>
%H A001426 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 A001426 <a href="Sindx_Se.html#semigroups">Index entries for sequences related 
               to semigroups</a>
%Y A001426 Cf. A001423, A023815, A027851, A058105, A058116.
%Y A001426 a(n) + A079193(n) + A079196(n) + A079199(n) = A001329(n).
%Y A001426 Sequence in context: A090363 A115086 A125276 this_sequence A059440 A020075 
               A020030
%Y A001426 Adjacent sequences: A001423 A001424 A001425 this_sequence A001427 A001428 
               A001429
%K A001426 nonn,nice,hard
%O A001426 0,3
%A A001426 N. J. A. Sloane (njas(AT)research.att.com).
%E A001426 a(8) (from the Satoh et al. paper) supplied by Richard Schroeppel, Jul 
               22 2005
%E A001426 a(9) and a(10) from Grillet references sent by Jens Zumbragel (jzumbr(AT)math.unizh.ch), 
               Jun 14 2006