On the number of collinear triples in permutations
Abstract
Description
Let $α:\mathbb{Z}_n\to\mathbb{Z}_n$ be a permutation and $Ψ(α)$ be the number of collinear triples modulo $n$ in the graph of $α$. Cooper and Solymosi had given by induction the bound $\min_αΨ(α)\geq\lceil(n-1)/4\rceil$ when $n$ is a prime number. The main purpose of this paper is to give a direct proof of that bound. Besides, the expected number of collinear triples a permutation can have is also been determined.
4 pages
4 pages