I want to find all the powers of 2 that have two digits. The smallest power of 2 that has two digits is $2^4 = 16$. The largest power of 2 that has two digits is $2^6 = 64$. So the possible values of $n$ are 4, 5, and 6. 
How many two-digit numbers can be written in the form $2^n$ where $n$ is an integer?