What is the radius of convergence of ∑n=1∞nnn!xn\sum_{n=1}^{\infty} \frac{n^n}{n!} x^n∑n=1∞n!nnxn?
R=eR = eR=e
R=1/eR = 1/eR=1/e
R=1R = 1R=1
R=∞R = \inftyR=∞