A118542 - OEIS

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A118542

Number of nonisomorphic groupoids with <= n elements.

1, 2, 12, 3342, 178985294, 2483527716080119, 14325590005802419238355799, 50976900301828909677297289506452525838, 155682086691137998248942804080553139214788341933547854 (list; graph; refs; listen; history; internal format)

	OFFSET	`0,2`
	COMMENTS	`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.`
	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 A074200 A048830` `Adjacent sequences: A118539 A118540 A118541 * A118543 A118544 A118545`
	KEYWORD	`nonn`
	AUTHOR	`Jonathan Vos Post (jvospost3(AT)gmail.com), May 06 2006`

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Last modified February 14 10:24 EST 2012. Contains 205614 sequences.