code: def bsn(self) -> str:
          
          def _is_valid_bsn(number: str) -> bool:
              total = 0
              multiplier = 9
  
              for char in number:
                  multiplier = -multiplier if multiplier == 1 else multiplier
                  total += int(char) * multiplier
                  multiplier -= 1
  
              result = total % 11 == 0
              return result
  
          a, b = (100000000, 999999999)
          sample = str(self.random.randint(a, b))
  
          while not _is_valid_bsn(sample):
              sample = str(self.random.randint(a, b))
  
          return sample
docs: Generate a random, but valid ``Burgerservicenummer``.
  
          :returns: Random BSN.
  
          :Example:
              255159705