A258720 Number of non-self-dual groupoids which are equal to their duals.

0, 3, 1596, 89460896, 1241763541901150, 7162795001623210170643008, 25488450150907291894372809845206177481, 77841043345568973636021232493841647618443964915982324, 270925719901279918478856582434909122129159229348142178651137261056627814

Offset: 1

Author

N. J. A. Sloane, Jun 18 2015

Keywords

• nonn

Links

• N. J. A. Sloane, Overview of A001329, A001423-A001428, A258719, A258720.
• T. Tamura, Some contributions of computation to semigroups and groupoids, pp. 229-261 of J. Leech, editor, Computational Problems in Abstract Algebra. Pergamon, Oxford, 1970. (Annotated and scanned copy)

Crossrefs

Cf. A001329, A001424, A029850, A258719.

Formula

a(n) = (A001329(n) - A029850(n))/2. - Andrew Howroyd, May 06 2023

Extensions

Terms a(5) and beyond from Andrew Howroyd, May 06 2023