Power of Four

Given an integer `n`, return _`true` if it is a power of four. Otherwise, return `false`_. An integer `n` is a power of four, if there exists an integer `x` such that `n == 4x`.   **Example 1:** **Input:** n = 16 **Output:** true ``` **Example 2:** **Input:** n = 5 **Output:** false ``` **Example 3:** **Input:** n = 1 **Output:** true ```   **Constraints:** - `-231 <= n <= 231 - 1`   **Follow up:** Could you solve it without loops/recursion?