A prime number is a number that is only evenly divisible by itself and $1.$ For example, the number $5$ is prime because it can only be evenly divided by $1$ and $5.$ The number $6,$ however, is not prime because it can be divided evenly by $1,2,3,$ and $6.$ Write a Boolean function named is$\_$prime which takes an integer as an argument and returns true if the argument is a prime number, or false otherwise. Use the function in a php program that prompts the user to enter a number then displays a message indicating whether the number is prime.