input: Write a function to determine if a number provided by the user is prime or not. If the number is prime, return "is a prime number" else return "is not a prime number". If the number provided is less than or equal to 1, return "is not a prime number".
  num = int(input('Enter a number: '))
  assert is_prime(17) == "is a prime number"
  assert is_prime(4) == "is not a prime number"
  assert is_prime(1) == "is not a prime number"
  assert is_prime(2) == "is a prime number"
  assert is_prime(-5) == "is not a prime number"
output: def is_prime(num):
      if num <= 1:
          return "is not a prime number"
      for i in range(2, int(num**0.5) + 1):
          if num % i == 0:
              return "is not a prime number"
      return "is a prime number"