text: #!/usr/bin/env python
  # -*- coding: utf-8 -*-
  """
  Finding the nth digit of the fractional part of the irrational number.
  """
  
  def digit_at(n):
      d = 1
      n -= 1
      while 1:
          """
          number of 1 digit numbers is 9
          number of 2 digit numbers is 90
          number of 3 digit numbers is 900
              ...
          number of d digit numbers is 9*10**(d-1)
          """
          ds = d * 9 * 10**(d - 1)
          if n > ds:
              n -= ds
          else:
              break
          d += 1
      num = n // d + 10**(d - 1)
      return int(str(num)[n % d])
  
  def pe40():
      """
      >>> pe40()
      210
      """
      d = 1
      for i in range(7):
          d *= digit_at(10**i)
          # print(digit_at(10**i))
      return d
  
  if __name__ == "__main__":
      import doctest
      doctest.testmod()
  