code: def prime3(a):
          
          if a < 2:
              return False
          if a == 2 or a == 3:
              return True  # manually test 2 and 3
          if a % 2 == 0 or a % 3 == 0:
              return False  # exclude multiples of 2 and 3
  
          max_divisor = int(math.ceil(a ** 0.5))
          d, i = 5, 2
          while d <= max_divisor:
              if a % d == 0:
                  return False
              d += i
              i = 6 - i  # this modifies 2 into 4 and vice versa
  
          return True
docs: Simple trial division prime detection
          :param a:
          :return: