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Coloring cuates

Source: Mexican Mathematical Olympiad 2014 Problem 1

November 11, 2014
combinatorics proposedcombinatorics

Problem Statement

Each of the integers from 1 to 4027 has been colored either green or red. Changing the color of a number is making it red if it was green and making it green if it was red. Two positive integers mm and nn are said to be cuates if either mn\frac{m}{n} or nm\frac{n}{m} is a prime number. A step consists in choosing two numbers that are cuates and changing the color of each of them. Show it is possible to apply a sequence of steps such that every integer from 1 to 2014 is green.