Definition:Divisor Count Function

Definition
Let $n$ be an integer such that $n \ge 1$.

The divisor count function is defined on $n$ as being the total number of positive integer divisors of $n$.

It is denoted on as $\sigma_0$ (the Greek letter sigma).

That is:
 * $\ds \map {\sigma_0} n = \sum_{d \mathop \divides n} 1$

where $\ds \sum_{d \mathop \divides n}$ is the sum over all divisors of $n$.

Also see

 * Definition:Divisor Function
 * Definition:Divisor Sum Function