Find the radius of convergence RRR of the series ∑n=1∞n!xnnn\sum_{n=1}^{\infty} \frac{n! x^n}{n^n}∑n=1∞nnn!xn.
R=1R = 1R=1
R=eR = eR=e
R=1/eR = 1/eR=1/e
R=∞R = \inftyR=∞