input: from typing import Union
  
  def is_prime_number(number: int) -> Union[bool, str]:
      """Determine if a given number is prime or not.
      >>> is_prime_number(17)
      True
      >>> is_prime_number(20)
      False
      """
      if number <= 1:
          return False
      for i in range(2, int(number ** 0.5) + 1):
          if number % i == 0:
              return False
      return True
output:     if number == 2:
          return True
      if number % 2 == 0:
          return False
      return "Invalid input"