MathDB
Hard NT with modular transformations

Source: Kvant Magazine No. 7 2023 M2757

January 9, 2024
number theorymodular arithmetic

Problem Statement

Let pp{} be a prime number. There are pp{} integers a0,,ap1a_0,\ldots,a_{p-1} around a circle. In one move, it is allowed to select some integer kk{} and replace the existing numbers via the operation aiaiai+ka_i\mapsto a_i-a_{i+k} where indices are taken modulo p.p{}. Find all pairs of natural numbers (m,n)(m, n) with n>1n>1 such that for any initial set of pp{} numbers, after performing any mm{} moves, the resulting pp{} numbers will all be divisible by n.n{}.
Proposed by P. Kozhevnikov