%I A118100
%S A118100 1,2,5,17,75,400,2543,19834,241639
%N A118100 Number of commutative semigroups of order <= n.
%C A118100 A001426(n) is the number of commutative semigroups of order n. A001426(n) 
               + A079193(n) + A079196(n) + A079199(n) = A001329(n). 2, 5, 17, 2543 
               and 241639 are primes.
%H A118100 <a href="Sindx_Se.html#semigroups">Index entries for sequences related 
               to semigroups</a>.
%F A118100 a(n) = SUM[i=1..n] A001426(i).
%e A118100 a(8) = 1 + 1 + 3 + 12 + 58 + 325 + 2143 + 17291 + 221805 = 241639.
%Y A118100 Cf. A001423, A001426, A023815, A027851, A058105, A058116.
%Y A118100 Sequence in context: A112831 A000774 A081046 this_sequence A129591 A099825 
               A014288
%Y A118100 Adjacent sequences: A118097 A118098 A118099 this_sequence A118101 A118102 
               A118103
%K A118100 nonn
%O A118100 0,2
%A A118100 Jonathan Vos Post (jvospost3(AT)gmail.com), May 11 2006