I need to calculate the sum :
$\sum_{k=1}^{n}\frac{1^2\space5^2\space...\space(4k-3)^2}{3^2\space7^2\space...\space(4k-1)^2}$
I am thinking of writing it as a difference of sums so when I do the difference some terms will reduce and we will get the first term from one and the last from the other one. Can you help me find out how to write it?