Use strong mathematical induction to prove that $a_n \le 2^n$ for each integer $n\ge 0$

Question

Let $a_0, a_1, a_2, .... $be the sequence defined recursively as

$a_0 = 1, a_1 = 2, a_k = a_{k-1} + a_{k-2}$ for each integer $k >=2$

I'm not sure how to work with sequences.