编写函数fun,函数的功能是：根据以下公式计算s,计算结果作为函数值返回；n通过形参传入。 s=1 + 1/(1+2) + 1/(1+2+3) +... + 1/(1+2+...+n) -Write a function fun, function is the function: according to the following formula s, calculated as a function return value n passing through the param