luogu1829 [国家集训队]Crash的数字表格

被 bs 了姿势水平……好好学习数学QAQQAQQAQ

ref

#include <iostream>
#include <cstring>
#include <cstdio>
using namespace std;
typedef long long ll;
int n, m, pri[10000005], cnt, mu[10000005], qia[10000005];
bool isp[10000005];
const int mod=20101009;
void shai(){
	memset(isp, true, sizeof(isp));
	isp[0] = isp[1] = false;
	mu[1] = 1;
	for(int i=2; i<=10000000; i++){
		if(isp[i])	pri[++cnt] = i, mu[i] = -1;
		for(int j=1; j<=cnt && i*pri[j]<=10000000; j++){
			isp[i*pri[j]] = false;
			if(i%pri[j]==0){
				mu[i*pri[j]] = 0;
				break;
			}
			mu[i*pri[j]] = mu[i] * -1;
		}
	}
	for(int i=1; i<=10000000; i++)
		qia[i] = ((ll)i*i*mu[i]%mod+mod)%mod;
	for(int i=2; i<=10000000; i++)
		qia[i] = (qia[i-1] + qia[i]) % mod;
}
int solve1(int x, int y){
	int i=1, re=0;
	while(i<=min(x, y)){
		int j=min(x/(x/i), y/(y/i));
		int tmp=(qia[j]-qia[i-1]+mod)%mod;
		tmp = (ll)tmp * ((ll)(1+x/i)*(x/i)/2 % mod) % mod;
		tmp = (ll)tmp * ((ll)(1+y/i)*(y/i)/2 % mod) % mod;
		re = (re + tmp) % mod;
		i = j + 1;
	}
	return re;
}
int main(){
	cin>>n>>m;
	shai();
	int i=1, ans=0;
	while(i<=min(n, m)){
		int j=min(n/(n/i), m/(m/i));
		int tmp=((ll)(i+j)*(j-i+1)/2)%mod;
		tmp = (ll)tmp * solve1(n/i, m/i) % mod;
		ans = (ans + tmp) % mod;
		i = j + 1;
	}
	cout<<ans<<endl;
	return 0;
}