bzoj2818【莫比乌斯函数】【线性筛】

#include<iostream>#include<algorithm>#include<cstdio>#include<cstdlib>#include<cstring>using namespace std;typedef long long LL;inline int read(){int x=0;bool f=0;char c=getchar();for (;c<'0'||c>'9';c=getchar()) f=c=='-'?1:0;for (;c>='0'&&c<='9';c=getchar()) x=x*10+c-'0';return f?-x:x;}const int N=10000010;int n,pr[N],pc=0,mu[N],f[N];bool np[N];LL ans=0;int main(){n=read();for (int i=2;i<=n;i++){if (!np[i]) pr[++pc]=i,mu[i]=-1,f[i]=1;for (int j=1,k=i<<1;j<=pc&&k<=n;k=i*pr[++j]){np[k]=1;if (i%pr[j]==0) {mu[k]=0;f[k]=mu[i];break;}mu[k]=-mu[i];f[k]=mu[i]-f[i];}}for (int i=1,dv;i<=n;i++)dv=n/i,ans+=(LL)dv*dv*f[i];printf("%lld\n",ans);return 0;}