Definition:Sum Over Divisors

Let $$n$$ be a positive integer.

Let $$f: \Z^*_+ \to \Z^*_+$$ be a function on the positive integers.

Let $$d \backslash n$$ denote that $$d$$ is a divisor of $$n$$.

Then the sum of $$f \left({d}\right)$$ over all the divisors of $$n$$ is denoted:
 * $$\sum_{d \backslash n} f \left({d}\right)$$.

Thus, for example:
 * $$\sum_{d \backslash 10} f \left({d}\right) = f \left({1}\right) + f \left({2}\right) + f \left({5}\right) + f \left({10}\right)$$.