MathDB
Annalena has infinitely many cowbells in each of n different colours

Source: Switzerland - 2022 Swiss Final Round p6

November 17, 2022
combinatoricsColoring

Problem Statement

Let n3n\ge 3 be an integer. Annalena has infinitely many cowbells in each of nn different colours. Given an integer mn+1m \ge n + 1 and a group of mm cows standing in a circle, she is tasked with tying one cowbell around the neck of every cow so that every group of n+1n + 1 consecutive cows have cowbells of all the possible nn colours. Prove that there are only finitely many values of mm for which this is not possible and determine the largest such mm in terms of nn.