Divisor -- from Wolfram MathWorld

A divisor, also called a factor, of a number n is a number d which divides n (written d|n). For integers, only positive divisors are usually considered, though obviously the negative of any positive divisor is itself a divisor. A list of (positive) divisors of a given integer n may be returned by the Wolfram Language function Divisors[n]. Sums and products are commonly taken over only some subset of values that are the divisors of a given number. Such a sum would then be denoted, for...