What is the number of digits of a power of 2?
2 ---> 1 digit
2 * 2 = 4 ---> 1 digit
2 * 2 * 2 = 8 ---> 1 digit
2 * 2 * 2 * 2 = 16 ---> 2 digits
...
...
...
2 * 2 * 2 * 2 * 2 * 2 * 2 * 2 * 2 * 2 = 1024 ---> 4 digits
Then, given the exponent, what would be the number of digits of that power?