What is the radius of convergence of ∑n=0∞n! xn\displaystyle\sum_{n=0}^{\infty} n!\, x^nn=0∑∞n!xn?
R=0R = 0R=0
R=1R = 1R=1
R=∞R = \inftyR=∞
R=eR = eR=e