Define a function is_prime that receives an integer argument and returns True if the argument is a prime number and otherwise returns False. (An integer is prime if it is greater than 1 and cannot be divided evenly [with no remainder] other than by itself and one. For example, 15 is not prime because it can be divided by 3 or 5 with no remainder. 13 is prime because only 1 and 13 divide it with no remainder.)