\begin{align*} a_0 \amp = 3\\ a_1 \amp = 4\\ a_2 \amp = 2\cdot 4 - 3 = 5\\ a_3 \amp = 2\cdot 5 - 4 = 6\\ a_4 \amp = 2\cdot 6 - 5 = 7\\ a_5 \amp = 2\cdot 7 - 6 = 8\\ a_6 \amp = 2\cdot 8 - 7 = 9 \end{align*}