If a sequence satisfies $a_n = 3a_{n-1} - 2a_{n-2}$, which value is the ratio of successive terms $\frac{a_n}{a_{n-1}}$ as $n \to \infty$ if $a_n = c_1(2^n) + c_2(1^n)$ and $c_1 \neq 0$?