Answer
$a_1=2,a_2=3, a_3= 7, a_4= 13, a_5= 27, $ neither.
Work Step by Step
Given $a_1=2,a_2=3, a_n=a_{n-1}+2a_{n-2}$, we have $a_3=a_2+2a_1=7, a_4=a_3+2a_2=13, a_5=a_4+2a_3=27, $ and we can identify the sequence as neither arithmetic nor geometric.
