\[a_{1} = 27;\ \ a_{n + 1} = \frac{81}{a_{n}}:\ \]
\[a_{2} = \frac{81}{27} = 3;\ \]
\[a_{3} = \frac{81}{3} = 27;\ \ \]
\[a_{4} = \frac{81}{27} = 3.\ \]