For which values of the exponent aaa does the series ∑n=1∞na3n\sum_{n=1}^{\infty} \frac{n^a}{3^n}∑n=1∞3nna converge?
Only for a<0a < 0a<0
Only for a=0a = 0a=0
For all real values of aaa (the exponential growth dominates any polynomial)
Only for a≤1a \leq 1a≤1