Answer
neither
Work Step by Step
$a_1=2(1)^3=2,a_2=2(2)^3=16,a_3=2(3)^3=54$
In order for a sequence to be geometric, the quotient of all consecutive terms must be constant.
Hence here: $16-2=14\ne54-16=38$, which is not constant thus it is not a geometric sequence.
In order for a sequence to be arithmetic, the difference of all consecutive terms must be constant.
Hence here: $16/2=8\ne54/16=3.375$, which is not constant thus it is not an arithmetic sequence.
Hence it is neither.