SP19985 GCDEX2 - GCD Extreme (hard)

This problem is a harder version of [GCDEX](../GCDEX). Let $$ G(n) = \sum _{i=1}^{n} \sum _{j=i+1}^{n} \gcd(i, j). $$ For example, $ G(1) = 0 $ , $ G(2) = \gcd(1, 2) = 1 $ , $ G(3) = \gcd(1, 2) + \gcd(1, 3) + \gcd(2, 3) = 3 $ . Given $ N $ , find $ G(N) $ **modulo** $ 2^{64} $ .

N/A

N/A