code: def _convert_number_to_subscript(num):
          
          subscript = ''
          for character in str(num):
              subscript += chr(0x2080 + int(character))
          return subscript
docs: Converts number into subscript
  
          input = ["a", "a1", "a2", "a3", "be2", "be3", "bad2", "bad3"]
          output = ["a", "a₁", "a₂", "a₃", "be₂", "be₃", "bad₂", "bad₃"]
  
          :param num: number called after sign
          :return: number in subscript