Definition:Divisor Count Function

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

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 known as
Some sources refer to this as the divisor function and denote it $d \left({n}\right)$, but as there is a more general definition of the divisor function the more precise name tau function is preferred.

Also see

 * Definition:Divisor Function