次方公式

\[\begin{aligned} \sum_{i = 1}^{n} i^2 & = \frac{n}{6} \times (n + 1) \times (2 \times n + 1) \\ \sum_{i = 1}^{n} i^3 & = (\sum_{i = 1}^{n} i)^2 \end{aligned}\]