Source: Israel Grosman Memorial Mathematical Olympiad 1999 p1
February 15, 2020
divisiblenumber theory
Problem Statement
For any 16 positive integers n,a1,a2,...,a15 we define T(n,a1,a2,...,a15)=(a1n+a2n+...+a15n)a1a2...a15.
Find the smallest n such that T(n,a1,a2,...,a15) is divisible by 15 for any choice of a1,a2,...,a15.