what is the 10th term of the sequence 64,16,4.....?

what is the 10th term of the sequence 64,16,4.....?

$$\small{\text{$ \begin{array}{rclcl} a_1 &=& 64 &=& 4^3 \\ a_2 &=& 16 &=& 4^2 \\ a_3 &=& 4 &=& 4^1 \\ && \cdots \\ a_n &&&=& 4^{4-n} \\ \\ \hline \\ a_{10} &&&=& 4^{4-10} \\ a_{10} &&&=& 4^{-6} \end{array} $}}$$