Source: Irish Mathematical Olympiad 2023 Problem 5
May 16, 2023
number theory
Problem Statement
The positive integers a,b,c,d satisfy(i) a+b+c+d=2023
(ii) 2023∣ab−cd
(iii) 2023∣a2+b2+c2+d2.Assuming that each of the numbers a,b,c,d is divisible by 7, prove that each of the numbers a,b,c,d is divisible by 17.