Visible Lattice Points SPOJ - VLATTICE

题意：

有一个n∗n∗n的三维直角坐标空间，问从(0,0,0)看能看到几个点。

题解：

本题是二维的一个升级版，升级成三维
用莫比乌斯反演来做

代码：

#include <bits/stdc++.h>
#include <unordered_map>
#define debug(a, b) printf("%s = %d\n", a, b);
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> PII;
clock_t startTime, endTime;
//Fe~Jozky
const ll INF_ll= 1e18;
const int INF_int= 0x3f3f3f3f;
void read(){};
template <typename _Tp, typename... _Tps> void read(_Tp& x, _Tps&... Ar)
{x= 0;char c= getchar();bool flag= 0;while (c < '0' || c > '9')flag|= (c == '-'), c= getchar();while (c >= '0' && c <= '9')x= (x << 3) + (x << 1) + (c ^ 48), c= getchar();if (flag)x= -x;read(Ar...);
}
template <typename T> inline void write(T x)
{if (x < 0) {x= ~(x - 1);putchar('-');}if (x > 9)write(x / 10);putchar(x % 10 + '0');
}
void rd_test()
{
#ifdef ONLINE_JUDGE
#elsestartTime = clock ();freopen("data.in", "r", stdin);
#endif
}
void Time_test()
{
#ifdef ONLINE_JUDGE
#elseendTime= clock();printf("\nRun Time:%lfs\n", (double)(endTime - startTime) / CLOCKS_PER_SEC);
#endif
}
const int maxn=1000020;
int mu[maxn];
int prime[maxn];
int vis[maxn];
int cnt=0;
void get_mu(int N){mu[1]=1;for(int i=2;i<=N;i++){if(!vis[i]){prime[++cnt]=i;mu[i]=-1;}for(int j=1;j<=cnt&&i*prime[j]<=N;j++){vis[i*prime[j]]=1;if(i%prime[j]==0)break;mu[i*prime[j]]=-mu[i];}}
} 
int main()
{//rd_test();get_mu(1000000);int t;read(t);while(t--){ll n;cin>>n;ll sum=3ll;for(int i=1;i<=n;i++){sum+=mu[i]*(1ll*n/i)*(n/i)*(n/i+3ll);}cout<<sum<<endl;}//Time_test();
}