NL-NWO 1965 Problem 1

We consider the sequence $t_1,t_2,t_3,...$ By $P_n$ we mean the product of the first $n$ terms of the sequence. Given that $t_{n+1} = t_n \cdot t_{n+2}$ for each $n$ , and that $P_{40} = P_{80} = 8$ . Calculate $t_1$ and $t_2$ .