A prime number and its same-colored multiples
Source: 2021 Iberoamerican Mathematical Olympiad, P1
October 20, 2021
setprime numbersnumber theory
Problem Statement
Let be a set of different prime numbers and let be the set of all the integers greater than so that their prime decomposition only contains primes of . The elements of are colored in such a way that:[*] each element of has a different color,
[*] if , then is the same color of or ,
[*] for any pair of different colors and , there are no (not necessarily distinct from one another), with colored and colored , so that is a divisor of and is a divisor of , simultaneously.Prove that there exists a prime of so that all its multiples in are the same color.