input: Write a python function to check if a number is a prime number.
  assert Number(2).is_prime() == True
  assert Number(3).is_prime() == True
  assert Number(4).is_prime() == False
  assert Number(17).is_prime() == True
  assert Number(18).is_prime() == False
output: class Number:
      def __init__(self, value):
          self.value = value
  
      def is_prime(self):
          if self.value < 2:
              return False
          for i in range(2, int(self.value ** 0.5) + 1):
              if self.value % i == 0:
                  return False
          return True