Answer
The sequence is not arithmetic.
Work Step by Step
We compute the difference between each term and the preceding term. If the difference is same, then the sequence is arithmetic.
$a_{2}-a_{1}=80-100=-20$
$a_{3}-a_{2}=64-80=-16$
$a_{4}-a_{3}=51.2-64=-12.8$
$a_{5}-a_{4}=40.96-51.2=-10.24$
$a_{6}-a_{5}=32.768-40.96=-8.192$
The difference between each term and preceding term is not constant and therefore the sequence is not arithmetic.