Assuming n is a nonnegative integer, what does the following recursive algorithm compute?

procedure power$($n: nonnegative integer$)$

if n $=0$ then power$($n$)$ : $=3$

else power$($n$)$ : $=$ power$($n $1)$ power$($n $1)$

$1.$ n$^2$

$2.3$n

$3.3^(2$n$)$

$4.$ None of the above