def factorial(n):
    """Calculate factorial recursively"""
    if n <= 1:
        return 1
    else:
        return n * factorial(n - 1)

def is_prime(num):
    if num < 2:
        return False
    for i in range(2, int(num ** 0.5) + 1):
        if num % i == 0:
            return False
    return True

# Test the functions
print(f"Factorial of 5: {factorial(5)}")

for n in [2, 3, 4, 17, 21]:
    print(f"{n} is prime: {is_prime(n)}")