求和公式

\(\sum_{i=1}^ni=\frac{n(n+1)}{2}\)

\(\sum_{i=1}^ni^2=\frac{n(n+1)(2n+1)}{6}\)

\(\sum_{i=1}^ni^3=\frac{n^2(n+1)^2}{4}\)

\(\sum_{i=1}^{n}i^4=\frac{n(n+1)(2n+1)(3n^2+3n-1)}{30}\)