bzoj 2818【モビウス関数】【線形ふるい】

#include
#include
#include
#include
#include
using namespace std;
typedef long long LL;
inline int read()
{
	int x=0;bool f=0;char c=getchar();
	for (;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
",ans);
	return 0;
}