51nod1225 余数之和

打表可以看出规律。分块求就可以了。

#include<cstdio>

#include<cstring>

#include<cctype>

#include<algorithm>

using namespace std;

#define ll long long

ll read(){

	ll x=0;char c=getchar();

	while(!isdigit(c)) c=getchar();

	while(isdigit(c)) x=x*10+c-'0',c=getchar();

	return x;

}

const ll mod=1e9+7;

const ll tt=5e8+4;

int main(){

	ll n=read(),last,ans=0;

	for(ll i=1;i<=n;i=last+1){

		last=n/(n/i);

		ans=(ans+(last-i+1)%mod*((n%i+n%last)%mod)%mod*tt%mod)%mod;

	}

	printf("%lld\n",ans);

	return 0;

}