competitve programming solution here...
An Interesting Sequence Problem Solution Code: CodeChef #include <bits/stdc++.h> using namespace std ; #define endl " \n " int main () { cin. tie ( 0 ); int N = 4 e 6 + 5 ; int phi[N], ans[N]; for ( int i = 0 ; i < N; i ++ ) { phi[i] = i; ans[i] = 0 ; } for ( int p = 2 ; p < N; p ++ ) { if (phi[p] == p) { phi[p] = p - 1 ; for ( int i = 2 * p; i < N; i += p) { phi[i] = (phi[i] / p) * (p - 1 ); } } } for ( int i = 1 ; i < N; i ++ ) { ans[i] += i - 1 ; for ( int j = 2 * i; j < N; j += i) { ans[j] += i * (( 1 + phi[j / i]) / 2 ); } } int t; cin >> t; while (t -- ) { int k; cin >> k; cout <&l