old_contents: from sequence import Sequence
  
  
  class Figurate(Sequence):
  
      _INCREMENT = None
  
      @classmethod
      def _append(cls):
          cls._NUMS.append(2 * cls._NUMS[-1] - cls._NUMS[-2] + cls._INCREMENT)
  
  
  class Triangle(Figurate):
  
      _NUMS = [1, 3]
      _INCREMENT = 1
  
  
  class Pentagonal(Figurate):
  
      _NUMS = [1, 5]
      _INCREMENT = 3
  
  
  class Hexagonal(Figurate):
  
      _NUMS = [1, 6]
      _INCREMENT = 4
  
new_contents: from sequence import Sequence
  
  
  class Figurate(Sequence):
      @classmethod
      def _append(cls):
          cls._NUMS.append(
              cls._NUMS[-1] * 2 - cls._NUMS[-2] +
              cls._NUMS[ 1] - 1 - cls._NUMS[ 0]
          )
  
  
  class Triangle(Figurate):
      _NUMS = [1, 3]
  
  
  class Pentagonal(Figurate):
      _NUMS = [1, 5]
  
  
  class Hexagonal(Figurate):
      _NUMS = [1, 6]
  
subject: Remove INCREMENT from Figurate