I can calculate the GCD of two numbers. given a set S = {1,2,3,4,5} and i have to calculate the GCD of each pair like {1,2} = 1, {1,3} =1 , {1,4} = 1, {1,5} = 1, {2,3} = 1, {2,4} = 2, {2,5} = 1 and so on. I know the O(N^2) solution by just simply calculate the GCD of each pair which will give me TLE in case of big set for 2<=n<= 10^9 or more but i want to learn O(N\*sqrt(N) ) solution or more better. i want the GCD of each pair separately.