4/(1*2*3)+7/(2*3*4)+.+(3n+1)/[n(n+1)(n+2)]
急吖
还有几个
1+1/(1+2)+1/(1+2+3)+.+1/(1+2+3+...+n)=
1/(根号下1+根号下2)+1/(根号下2+根号下3)+1/(根号下3+根号下4)+...+1/(根号下n+根号下n+1)=
1/3+1/(3+5)+1/(3+5+7)+.+1/(3+5+7+...+2n+1)=