Write a function, is_prime, that takes in a number as an argument. The function should return a boolean indicating whether or not the given number is prime.
A prime number is a number that is only divisible by two distinct numbers: 1 and itself.
For example, 7 is a prime because it is only divisible by 1 and 7. For example, 6 is not a prime because it is divisible by 1, 2, 3, and 6.
You can assume that the input number is a positive integer.
is_prime(2) # -> True
is_prime(3) # -> True
is_prime(4) # -> False
is_prime(5) # -> True
is_prime(6) # -> False
is_prime(7) # -> True
is_prime(8) # -> False
is_prime(25) # -> False
is_prime(31) # -> True
is_prime(2017) # -> True
is_prime(2048) # -> False
is_prime(1) # -> False
is_prime(713) # -> False