Crash的数字表格 / JZPTAB

https://www.cnblogs.com/peng-ym/p/8666124.html

#include<bits/stdc++.h>
#define LL long long
#define ULL unsigned long long
#define rep(i,j,k) for(int i=j;i<=k;i++)
#define dep(i,j,k) for(int i=k;i>=j;i--)
#define INF 0x3f3f3f3f
#define mem(i,j) memset(i,j,sizeof(i))
#define make(i,j) make_pair(i,j)
#define pb push_back
using namespace std;
const LL mod=;
const int N=1e7+;
int pre[N],tot,k;
LL mu[N];
bool vis[N];
void init() {
    mu[]=;
    rep(i,,N-) {
        if(!vis[i]) { pre[++tot]=i; mu[i]=-; }
        for(int j=;j<=tot&&pre[j]*i<=N-;j++) {
            vis[i*pre[j]]=;
            if(i%pre[j]==) break;
            mu[i*pre[j]]=-mu[i];
        }
    }
    rep(i,,N-) mu[i]=(mu[i-]+1LL*mu[i]*1LL*i%mod*1LL*i%mod)%mod;
}
int main() {
    int n,m;
    init();
    scanf("%d %d",&n,&m);
    LL ans=;
    LL inv2=(mod+1LL)/2LL;
    rep(d,,min(n,m)) {
        int M=m/d; int N=n/d;
        LL tmp=0LL;
        for(int l=,r;l<=min(N,M);l=r+) {
            r=min(N/(N/l),M/(M/l));
            tmp=(tmp+((mu[r]-mu[l-])%mod*1LL*(1LL+N/l)%mod*1LL*(N/l)%mod*inv2%mod*(1LL+M/l)%mod*(M/l)%mod*inv2%mod)%mod)%mod;
        }
        ans=(ans+tmp*1LL*d%mod)%mod;
    }
    printf("%lld\n",(ans+mod)%mod);
    return ;
}