A090600 - OEIS

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).

1, 2, 30, 22456, 3179460875, 118459556737869096, 1841479754519556293280702095, 17699004125822025124951660289473617122688, 146207646053305863964379580591072585873215024249550168360

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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

Table of n, a(n) for n=1..9.

Eric Postpischil Posting to sci.math newsgroup, May 21 1990

Eric Weisstein's World of Mathematics, Groupoid.

Index entries for sequences related to groupoids

FORMULA

a(n) = (A090601(n) + A090604(n))/2