Chapter 11 - Sequences; Induction; the Binomial Theorem - Section 11.1 Sequences - 11.1 Assess Your Understanding - Page 827: 43

$ a_1=1\\ a_2=2 \\a_3=2 \\ a_4=4 \\ a_5=8$

We are given that $a_n=(a_{n-1}) (a_{n-2})$ and $a_1=1; a_2=2$. In order to determine the remaining values, we will have to substitute $n=3,4,5$ into the given sequence. We use previous terms to compute successive terms as follows: $ a_3=(a_2)(a_1)=(2)(1)=2 \\ a_4=(a_3)(a_2)=(2)(2)=4 \\ a_5=(a_4)(a_3)=(4)(2)=8$