Сумматоры

class Summator:
    def transform(self, n):
        return n
    def sum(self, N):
        return sum([self.transform[i] for i in range(1, N)])

class SquareSummator(Summator):
    def transform(self, n):
        return n**2

class CubeSummator(Summator):
    def transform(self, n):
        return n**3