What is the interval of convergence for ∑n=1∞n!nnxn\sum_{n=1}^{\infty} \frac{n!}{n^n} x^n∑n=1∞nnn!xn?
(−e,e)(-e, e)(−e,e)
(−1,1)(-1, 1)(−1,1)
[−e,e][-e, e][−e,e]
All real numbers