数学公式

$1*n + 2 * (n - 1) + 3 * (n - 2) + ...... + n * 1 = \frac{n * (n + 1) * (n + 2)}{6}$
$1^2 + 2^2 + 3^2 + ...... + n^2 = \frac{n * (n + 1) * (2n + 1)}{6}$
$1^3 + 2^3 + 3^3 + ...... + n^3 = \frac{n^2 * (n + 1)^2}{4}$