**Solution**

**Power of Four** https://leetcode.com/problems/power-of-four/

**Algorithm**

- Must also be a power of 2 and have just one set bit. Use n&(n-1).
- Only the even numbered bit should be set like 2^2 or 2^4 or 2^6. Use mask 0x55555555.
- Notice 0x55555555 is: 01010101010101010101010101010101. num & mask != 0.

```
class Solution(object):
def isPowerOfFour(self, num):
"""
:type num: int
:rtype: bool
"""
if num == 1:
return True
val = 1
mask = 0x55555555
return (num&(num-1) == 0) and ((num & mask) != 0)
```