\[a_{n} = 2^{n - 3}\]
\[a_{1} = - 2^{1 - 3} = - 2^{- 2} = - \frac{1}{4}\]
\[a_{2} = - 2^{2 - 3} = - 2^{- 1} = - \frac{1}{2}\]
\[a_{3} = - 2^{3 - 3} = - 2^{0} = - 1\]
\[a_{4} = - 2^{4 - 3} = - 2^{1} = - 2\]
\[a_{5} = - 2^{5 - 3} = - 2^{2} = - 4\]