0,2

The number of isomorphism classes of closed binary operations on sets of order <= n. See formulae by Christian G. Bower in A001329 Number of nonisomorphic groupoids with n elements.

a(n) = SUM[i=0..n] A001329(i). a(n) = SUM[i=0..n] (A079173(i)+A027851(i)). a(n) = SUM[i=0..n] (A079177(i)+A079180(i)). a(n) = SUM[i=0..n] (A079183(i)+A001425(i)). a(n) = SUM[i=0..n] (A079187(i)+A079190(i)). a(n) = SUM[i=0..n] (A079193(i)+A079196(i)+A079199(i)+A001426(i)).

a(5) = 1 + 1 + 10 + 3330 + 178981952 + 2483527537094825 = 2483527716080119 is prime.

Cf. A001424, A001425, A002489, A006448, A029850, A030245-A030265, A030271, A038015-A038023.

Sequence in context: A050649 A003042 A000887 this_sequence A007155 A074200 A048830

Adjacent sequences: A118539 A118540 A118541 this_sequence A118543 A118544 A118545

nonn

Jonathan Vos Post (jvospost3(AT)gmail.com), May 06 2006