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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

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

CROSSREFS

Sequence in context: A077521 A272445 A203309 * A113511 A292048 A062008

Adjacent sequences:  A090597 A090598 A090599 * A090601 A090602 A090603

KEYWORD

nonn

AUTHOR

Christian G. Bower, Dec 05 2003

STATUS

approved

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Last modified March 31 16:43 EDT 2020. Contains 333151 sequences. (Running on oeis4.)