MathDB
JBMO Shortlist 2020 N3

Source: JBMO Shortlist 2020

July 4, 2021
JuniorBalkanshortlist2020number theory

Problem Statement

Find the largest integer kk (k2k \ge 2), for which there exists an integer nn (nkn \ge k) such that from any collection of nn consecutive positive integers one can always choose kk numbers, which verify the following conditions:
1. each chosen number is not divisible by 66, by 77, nor by 88; 2. the positive difference of any two distinct chosen numbers is not divisible by at least one of the numbers 66, 77, and 88.