[HYSBZ\BZOJ2818][CQBZOJ2525]Gcd(最大公因数)

#include<cstdio>
#include<algorithm>
using namespace std;
#define MAXN 10000000
int mu[MAXN+10],p[MAXN+10],pcnt,n,sum[MAXN+10];
long long ans;
bool f[MAXN+10];
void Read(int &x){
char c;
while(c=getchar(),c!=EOF)
if(c>='0'&&c<='9'){
x=c-'0';
while(c=getchar(),c>='0'&&c<='9')
x=x*10+c-'0';
ungetc(c,stdin);
return;
}
}
void prepare(){
int i,j;
mu[1]=1;
for(i=2;i<=n;i++){
if(!f[i])
p[++pcnt]=i,mu[i]=-1,sum[i]=1;
for(j=1;p[j]*i<=n;j++){
f[p[j]*i]=1;
if(i%p[j]==0){
mu[i*p[j]]=0;
sum[i*p[j]]=mu[i];
break;
}
mu[i*p[j]]=-mu[i];
sum[i*p[j]]=mu[i]-sum[i];
}
sum[i]+=sum[i-1];
}
}
void solve(){
int i,last;
for(i=1;i<=n;i=last+1){
last=n/(n/i);
ans+=1ll*(sum[last]-sum[i-1])*(n/i)*(n/i);
}
}
int main()
{
Read(n);
prepare();
solve();
printf("%lld",ans);
}