Find $\lim\limits_{n \to \infty}\dfrac{x_n}{n}$ where $x_n = \sqrt[n]{1 + \sum\limits_{k=2}^n(k-1)(k-1)!}$
I need help to advance in the resolution of that limit: $ \lim_{n \to \infty}{\sqrt[n]{\frac{n!}{n^n}}} $