Visible Lattice Points SPOJ

#include<bits/stdc++.h>
#define ll long long
using namespace std;
const int maxn=1e7+10;
int vis[maxn];
int mu[maxn];
int prime[maxn];
int tot=0;
int sum1[maxn];
int sum2[maxn];
void get_mu()
{
    mu[1]=1; vis[1]=1;
    for(int i=2;i<maxn;i++)
    {
        if(!vis[i]) {mu[i]=-1; prime[++tot]=i; }
        for(int j=1;j<=tot && i*prime[j]<maxn;j++)
        {
            vis[i*prime[j]]=1;
            if(i%prime[j]==0) break;
            mu[i*prime[j]]=-mu[i];
        }
    }
    for(int i=1;i<maxn;i++)
        sum2[i]=sum2[i-1]+mu[i];
}
int main()
{
    get_mu();
    int T; cin>>T;
    while(T--)
    {
        int n; cin>>n;
        ll ans=0;
        for(int l=1,r;l<=n;l=r+1)
        {
            r=n/(n/l);
            ans+=(sum2[r]-sum2[l-1])*1ll*(n/l)*(n/l)*(n/l);
            ans+=(sum2[r]-sum2[l-1])*1ll*(n/l)*(n/l)*3;
        }
        cout<<ans+3<<endl;
    }
}