OFFSET
0,2
COMMENTS
The number of isomorphism classes of closed binary operations on sets of order <= n. See formulas by Christian G. Bower in A001329 Number of nonisomorphic groupoids with n elements.
FORMULA
EXAMPLE
a(5) = 1 + 1 + 10 + 3330 + 178981952 + 2483527537094825 = 2483527716080119 is prime.
CROSSREFS
KEYWORD
nonn
AUTHOR
Jonathan Vos Post, May 06 2006
STATUS
approved