MathDB
Block-similar polynomials

Source: IMO 2015 Shortlist, A6

July 7, 2016
algebrapolynomialIMO Shortlist

Problem Statement

Let nn be a fixed integer with n2n \ge 2. We say that two polynomials PP and QQ with real coefficients are block-similar if for each i{1,2,,n}i \in \{1, 2, \ldots, n\} the sequences
\begin{eqnarray*} P(2015i), P(2015i - 1), \ldots, P(2015i - 2014) & \text{and}\\ Q(2015i), Q(2015i - 1), \ldots, Q(2015i - 2014) \end{eqnarray*}
are permutations of each other.
(a) Prove that there exist distinct block-similar polynomials of degree n+1n + 1. (b) Prove that there do not exist distinct block-similar polynomials of degree nn.
Proposed by David Arthur, Canada