16. Proper divisors

A divisor of a number N is any number that divides evenly into N. For example, the divisors of 12 are {1, 2, 4, 6, 12}.

The proper divisors of a number N are N's divisors, not including N itself. For example, the proper divisors of 12 are {1, 2, 4, 6}.

Write a program that finds a number's proper divisors.