What is the value of following expression  [math]\dfrac1{2^2-1}+\dfrac1{4^2-1}+\dfrac1{6^2-1}+\cdots\dfrac1{20^2-1}[/math]?
What is [math]\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{5^2}+\frac{1}{7^2}+\frac{1}{11^2}+ \cdots[/math]?