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Colourings of integers and power-of-two differences (BxMO 2023, Problem 2)

Source: BxMO 2023, Problem 2

May 6, 2023
BxMOcombinatorics

Problem Statement

Determine all integers k1k\geqslant 1 with the following property: given kk different colours, if each integer is coloured in one of these kk colours, then there must exist integers a1<a2<<a2023a_1<a_2<\cdots<a_{2023} of the same colour such that the differences a2a1,a3a2,,a2023a2022a_2-a_1,a_3-a_2,\dots,a_{2023}-a_{2022} are all powers of 22.