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A090600 Number of n-element groupoids with an identity, considered to be equivalent when they are isomorphic or anti-isomorphic (by reversal of the operator). 0
1, 2, 30, 22456, 3179460875, 118459556737869096, 1841479754519556293280702095, 17699004125822025124951660289473617122688, 146207646053305863964379580591072585873215024249550168360 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
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 Weisstein's World of Mathematics, Groupoid.
FORMULA
a(n) = (A090601(n) + A090604(n))/2
CROSSREFS
Sequence in context: A272445 A203309 A371205 * A113511 A292048 A062008
KEYWORD
nonn
AUTHOR
Christian G. Bower, Dec 05 2003
STATUS
approved

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Last modified March 28 16:58 EDT 2024. Contains 371254 sequences. (Running on oeis4.)