What is the interval of convergence for the series ∑n=1∞xnnn\sum_{n=1}^{\infty} \frac{x^n}{n^n}∑n=1∞nnxn?
(−1,1)(-1, 1)(−1,1)
[−1,1][ -1, 1 ][−1,1]
(−∞,∞)(-\infty, \infty)(−∞,∞)
(−e,e)(-e, e)(−e,e)