Playing a game of musical chairs
Source: 2023 Dutch BxMO TST, Problem 3
March 12, 2024
combinatorics
Problem Statement
We play a game of musical chairs with chairs numbered to . You attach leaves, numbered to , to the chairs in such a way that the number on a leaf does not match the number on the chair it is attached to. One player sits on each chair. Every time you clap, each player looks at the number on the leaf attached to his current seat and moves to sit on the seat with that number. Prove that, for any that is not a prime power with, it is possible to attach the leaves to the seats in such a way that after claps everyone has returned to the chair they started on for the first time.