Definition:Divisor Count Function

Definition
Let $n$ be an integer such that $n \ge 2$.

The $\tau$ (tau) function is defined on $n$ as being the total number of positive integer divisors of $n$.

That is:
 * $\displaystyle \tau \left({n}\right) = \sum_{d \mathop \backslash n} 1$

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

Also see

 * Definition:Divisor Function