text: # ch9/example1.py
  
  from math import sqrt
  
  def is_prime(x):
      print('Processing %i...' % x)
  
      if x < 2:
          print('%i is not a prime number.' % x)
  
      elif x == 2:
          print('%i is a prime number.' % x)
  
      elif x % 2 == 0:
          print('%i is not a prime number.' % x)
  
      else:
          limit = int(sqrt(x)) + 1
          for i in range(3, limit, 2):
              if x % i == 0:
                  print('%i is not a prime number.' % x)
                  return
  
          print('%i is a prime number.' % x)
  
  if __name__ == '__main__':
  
      is_prime(9637529763296797)
      is_prime(427920331)
      is_prime(157)
  