Source: 2017 Polish Junior Math Olympiad Second Round
May 22, 2023
number theory
Problem Statement
Do numbers x1,x2,…,x99 exist, where each of them is equal to 2+1 or 2−1, and satisfy the equation x1x2+x2x3+x3x4+…+x98x99+x99x1=199? Justify your answer.