MathDB
Painting Beads on Necklace

Source: 2021 ISL C2

July 12, 2022
IMO Shortlistpigeonhole principleISL 2021c2

Problem Statement

Let n3n\ge 3 be a fixed integer. There are mn+1m\ge n+1 beads on a circular necklace. You wish to paint the beads using nn colors, such that among any n+1n+1 consecutive beads every color appears at least once. Find the largest value of mm for which this task is \emph{not} possible.
Carl Schildkraut, USA