Function and Triangle are Best Friend

Algebra Level 4

A function is defined as $f(1) = 2017$ and $f(1) + f(2) + \cdots + f(n) = n^2 f(n)$ for all $n > 1$ . Find $f(2017)$ .

If you answer can be expressed as $\frac{a}{b}$ , where $a$ and $b$ are coprime positive integers, compute $a+b$ .