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arXiv · 1510.05987

Additive triples of bijections, or the toroidal semiqueens problem

Sean Eberhard·Freddie Manners·Rudi Mrazović
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Abstract

We prove an asymptotic for the number of additive triples of bijections $\{1,\dots,n\}\to\mathbb{Z}/n\mathbb{Z}$, that is, the number of pairs of bijections $\pi_1,\pi_2\colon \{1,\dots,n\}\to\mathbb{Z}/n\mathbb{Z}$ such that the pointwise sum $\pi_1+\pi_2$ is also a bijection. This problem is equivalent to counting the number of orthomorphisms or complete mappings of $\mathbb{Z}/n\mathbb{Z}$, to counting the number of arrangements of $n$ mutually nonattacking semiqueens on an $n\times n$ toroidal chessboard, and to counting the number of transversals in a cyclic Latin square. The method of proof is a version of the Hardy--Littlewood circle method from analytic number theory, adapted to the group $(\mathbb{Z}/n\mathbb{Z})^n$.

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Sean Eberhard, Freddie Manners, Rudi Mrazović. 2015-10-20. Additive triples of bijections, or the toroidal semiqueens problem. https://doi.org/10.4171/jems%2F841

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