private static boolean  isNumberAPrimeNumber(int userInput) {

        boolean isPrimeNumber = true;

        // check if userInput is divisible by 2 (which would make the value an even number)
        if (userInput % 2 == 0) return false;

        // prime number must be greater than 1, therefore int is assigned the starting value of 2.
        for(int i = 2; i < userInput; i++) {

            if(userInput % i == 0) isPrimeNumber = false;

        }

        return isPrimeNumber;
    }