code: def regon(self):
          
          voivodeship_number = self.random_int(0, 49) * 2 + 1
          regon_digits = [int(voivodeship_number / 10), voivodeship_number % 10]
  
          for _ in range(6):
              regon_digits.append(self.random_digit())
  
          regon_digits.append(regon_checksum(regon_digits))
  
          return ''.join(str(digit) for digit in regon_digits)
docs: Returns 9 character Polish National Business Registry Number,
          Polish: Rejestr Gospodarki Narodowej - REGON.
  
          https://pl.wikipedia.org/wiki/REGON