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 A118127 Number of quasigroups of order <= n. 0
 1, 2, 3, 8, 43, 1454, 1131985, 12199587820, 2697830531268481, 15224736759268778589978, 2750892227033887206264514123491 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS A quasigroup is a groupoid G such that for all a and b in G, there exist unique c and d in G such that ac = b and da = b. Hence a quasigroup is not required to have an identity element, nor be associative. Equivalently, one can state that quasigroups are precisely groupoids whose multiplication tables are Latin squares (possibly empty). LINKS FORMULA a(n) = SUM[i=0..n] A057991(i). EXAMPLE a(10) = 2750892227033887206264514123491 = 1 + 1 + 1 + 5 + 35 + 1411 + 1130531 + 12198455835 + 2697818331680661 + 15224734061438247321497 + 2750892211809150446995735533513. CROSSREFS Cf. A002860, A057991-A057994, A057771, A057996, A118641. Sequence in context: A127005 A042553 A042139 * A100644 A013208 A094370 Adjacent sequences:  A118124 A118125 A118126 * A118128 A118129 A118130 KEYWORD nonn AUTHOR Jonathan Vos Post, May 12 2006 STATUS approved

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Last modified January 28 03:49 EST 2020. Contains 331317 sequences. (Running on oeis4.)