2. In the sequence $\left\{a_{n}\right\}$, $a_{1}=2, a_{2}=7, a_{n+2}$ is equal to the unit digit of $a_{n+1} a_{n}$, then $a_{2009}=$
2. 2 Detailed Explanation: The first few terms are $2,7,4,8,2,6,2,2,4,8,2$, starting from the third term, it has a cycle of 6, so $a_{2009}=a_{6 \times 334+5}=a_{5}=2$.