Given an array of integers $$$(A[i] <= 10^5)$$$. We have to find number of unordered pairs (i, j) such that their GCD is greater than B.

All value <= $$$10^5$$$

Can someone give me a general idea how to approach such kinds of problems? Because this type of question appears frequently in programming contests and every time I devote much time solving this but failed each time :(