Answer
$a_n=256\cdot(0.25)^{n-1}$
Work Step by Step
The nth term of a geometric series can be obtained by the following formula: $a_n=a_1\cdot r^{n-1}$, where $a_1$ is the first term and $r$ is the common ratio.
Here the common ratio is $64/256=0.25$ and $a_1=256$.
Hence here $a_n=256\cdot(0.25)^{n-1}$
