A128934 - OEIS

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A128934

Number of centrist groupoids with n elements.

1, 0, 0, 58, 6634, 0

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OFFSET

1,4

COMMENTS

Systems with a binary operation that satisfies AB.BA=B. The rule is anti-commutative. Any central groupoid is centrist.

For comparison, a central groupoid is a system with a binary operator that satisfies the equation AB.BC=B (or (AB)(BC)=B). These have the curious property that the finite systems have a square number of elements. What is the beginning of the sequence giving the number of central groupoids of order n^2?

LINKS

Table of n, a(n) for n=1..6.

CROSSREFS

Sequence in context: A250919 A282438 A308391 * A173955 A243466 A201988

Adjacent sequences: A128931 A128932 A128933 * A128935 A128936 A128937

KEYWORD

nonn,more

AUTHOR

N. J. A. Sloane, Apr 28 2007, based on email from Richard C. Schroeppel (rcs(AT)CS.Arizona.EDU), Mar 15 2007.

STATUS

approved