Answer
$a_1=5, a_2=3, a_3= 18, a_4= 27, a_5= 81, $ neither.
Work Step by Step
1. Given $a_1=5, a_2=3, a_n=a_{n-1}+3a_{n-2}$, we have: $a_3=a_{2}+3a_{1}=18, a_4=a_{3}+3a_{2}=27, a_5=a_{4}+3a_{3}=81, $
2. We can identify the sequence as neither arithmetic nor geometric.
