Answer
Geometric sequence.
Work Step by Step
In order for a sequence to be geometric, the quotient of all consecutive terms must be constant.
Here: $\frac{a_{n+1}}{a_n}=\frac{2^{n+1}}{2^n}=\frac{2^n\cdot2}{2^n}=2$
Thus we can see that the quotient is constant, thus it is a geometric sequence.