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The number of transversals in a Latin square
Authors:Brendan D. McKay  Jeanette C. McLeod  Ian M. Wanless
Affiliation:(1) Computer Science Department, Australian National University, Canberra, ACT, 0200, Australia;(2) School of Mathematical Sciences, Monash University, Vic, 3800, Australia
Abstract:A Latin Square of order n is an n × n array of n symbols, in which each symbol occurs exactly once in each row and column. A transversal is a set of n entries, one selected from each row and each column of a Latin Square of order n such that no two entries contain the same symbol. Define T(n) to be the maximum number of transversals over all Latin squares of order n. We show that $$b^n leq T(n) leq c^nsqrt{n},n!$$ for n ≥ 5, where b ≈ 1.719 and c ≈ 0.614. A corollary of this result is an upper bound on the number of placements of n non-attacking queens on an n × n toroidal chess board. Some divisibility properties of the number of transversals in Latin squares based on finite groups are established. We also provide data from a computer enumeration of transversals in all Latin Squares of order at most 9, all groups of order at most 23 and all possible turn-squares of order 14.
Keywords:Transversal  Latin square   n-queens  Turn-square  Cayley table
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