Tinh phi

void tinhphi() {
       phi[1] = 1;
for (int i=2; i<MAXN; i++){
        if (!phi[i]){
            phi[i] = i-1;
            for (int j = (i<<1); j<MAXN; j+=i){
                if (!phi[j])
                    phi[j] = j;
                phi[j] = (phi[j]/i)*(i-1);
        }
    }
  }
}
// MAXN=1e6+5