Find the sum of the series ∑n=0∞(−1)nn!⋅3n\sum_{n=0}^{\infty} \frac{(-1)^n}{n! \cdot 3^n}∑n=0∞n!⋅3n(−1)n.
e1/3e^{1/3}e1/3
e−1/3e^{-1/3}e−1/3
e−3e^{-3}e−3
1/e31/e^31/e3