%I A027851
%S A027851 1,1,5,24,188,1915,28634,1627672
%N A027851 Number of nonisomorphic semigroups of order n.
%H A027851 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 A027851 C. Noebauer, <a href="http://www.algebra.uni-linz.ac.at/~noebsi/">Home 
               page</a>
%H A027851 C. Noebauer, <a href="ftp://www.algebra.uni-linz.ac.at/pub/noebauer/smallrings.ps.gz">
               The Numbers of Small Rings</a>
%H A027851 C. Noebauer, <a href="ftp://www.algebra.uni-linz.ac.at/pub/noebauer/thesis.ps.gz">
               Thesis on the enumeration of near-rings</a>
%H A027851 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 A027851 <a href="Sindx_Se.html#semigroups">Index entries for sequences related 
               to semigroups</a>
%Y A027851 a(n)=A001423(n)*2-A029851(n). Cf. A001426, A023814, A058108.
%Y A027851 a(n)+A079173(n)=A001329(n)
%Y A027851 Sequence in context: A009424 A009601 A009676 this_sequence A120765 A051812 
               A003224
%Y A027851 Adjacent sequences: A027848 A027849 A027850 this_sequence A027852 A027853 
               A027854
%K A027851 nonn,hard,nice
%O A027851 0,3
%A A027851 Christian G. Bower (bowerc(AT)usa.net), Dec 13 1997, updated Feb 19 2001