What is the recursive rule for this geometric sequence?−64,−16,−4,−1,...Enter your answers in the boxes.

[tex] a_n=\left\{\begin{array}{ccc}a_1=-64\\a_{n+1}=a_n:4\end{array}\right\\\\check:\\a_1=-64\\a_2=a_1:4\to a_2=-64:4=-16-OK\\a_3=a_2:4\to a_2=-16:4=-4-OK\\a_4=a_3:4\to a_4=-4:4=-1-OK\\\vdots [/tex]