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A118542 Number of nonisomorphic groupoids with <= n elements. 0
1, 2, 12, 3342, 178985294, 2483527716080119, 14325590005802419238355799, 50976900301828909677297289506452525838, 155682086691137998248942804080553139214788341933547854 (list; graph; refs; listen; history; text; internal format)
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.

LINKS

Table of n, a(n) for n=0..8.

FORMULA

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)).

EXAMPLE

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

CROSSREFS

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

Sequence in context: A050649 A003042 A000887 * A007155 A265092 A262032

Adjacent sequences:  A118539 A118540 A118541 * A118543 A118544 A118545

KEYWORD

nonn

AUTHOR

Jonathan Vos Post, May 06 2006

STATUS

approved

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Last modified October 18 23:39 EDT 2019. Contains 328211 sequences. (Running on oeis4.)