4 |n if a_1a_2 + a_2a_3 + ··· + a_{n-1}a_n + a_na_1 = 0, for a_i \in {1,-1}
Source: Portugal OPM 1999 p5
May 18, 2024
number theorySumalgebra
Problem Statement
Each of the numbers is equal to or . If , proves that is divisible by .