Find the value of $\frac{\frac 12 . \frac 22}{1^3} + \frac{\frac 22 . \frac 32}{1^3 + 2^3} + \frac{\frac 32 \frac 42}{1^3 + 2^3 + 3^3}$ upto n terms
What is the formula for $\frac{1}{1\cdot 2}+\frac{1}{2\cdot 3}+\frac{1}{3\cdot 4}+\cdots +\frac{1}{n(n+1)}$