What is the radius of convergence for ∑n=0∞n! xn(2n)!\sum_{n=0}^{\infty} \frac{n! \, x^n}{(2n)!}∑n=0∞(2n)!n!xn?
R=0R = 0R=0
R=1R = 1R=1
R=4R = 4R=4
R=∞R = \inftyR=∞