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Number of n-element groupoids with an identity, considered to be equivalent when they are isomorphic or anti-isomorphic (by reversal of the operator).

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1, 2, 30, 22456, 3179460875, 118459556737869096, 1841479754519556293280702095, 17699004125822025124951660289473617122688, 146207646053305863964379580591072585873215024249550168360 (list; graph; listen)

	OFFSET	`1,2`
	COMMENT	`Also partial groupoids with n-1 elements or groupoids with an absorbant (zero) element with n elements in each case the same equivalence.`
	LINKS	`Eric Postpischil Posting to sci.math newsgroup, May 21 1990` `Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.` `Index entries for sequences related to groupoids`
	FORMULA	`a(n) = (A090601(n) + A090604(n))/2`
	CROSSREFS	`Sequence in context: A000187 A053851 A077521 this_sequence A113511 A062008 A091776` `Adjacent sequences: A090597 A090598 A090599 this_sequence A090601 A090602 A090603`
	KEYWORD	`nonn`
	AUTHOR	`Christian G. Bower (bowerc(AT)usa.net), Dec 05 2003`

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Last modified November 25 20:09 EST 2009. Contains 167514 sequences.

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