def is_prime(n):
    """Efficiently check if a number n is prime."""
    if n <= 1:
        return False
    for i in range(2, int(n**0.5) + 1):
        if n % i == 0:
            return False
    return True

def main():
    print("Is 7 prime?", is_prime(7))
    # Add your code here to test other numbers or interact with the user.
    while True:
        try:
            number = int(input("Enter a positive integer (enter 'q' to quit): "))
            if number == "q":
                break
            print(f"Is {number} prime? {is_prime(number)}")
        except ValueError:
            print("Invalid input. Please enter an integer.")

if __name__ == "__main__":
    main()