An algebra problem by A Former Brilliant Member

Since the 16th term is the middle term, we can use the : Geometric Mean formula.

$a_{16}=\sqrt{(3)(3221225472)}$ $=98304$

Alternate solution:

$a_n=a_kr^{n-k}$

$3221225472=(3)r^{31-1}$

$r=2$

$a_{16}=(3)(2^{15})=98304$