hdu6715

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链接:hdu6715

题解

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#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<cstring>
#include<algorithm>
#define rep(i,x,y) for(register int i=x;i<=y;++i)
#define repd(i,x,y) for(register int i=x;i>=y;--i)
#define ll long long
using namespace std;
const int N=2e6+7;
ll mu[N],p[N],vis[N],cnt,n,m,T,a[N];
ll ans;
void get_mu(int n){
    mu[1]=1;
    rep(i,2,n){
        if(!vis[i])mu[i]=-1,p[++cnt]=i;
        for(int j=1;j<=cnt&&i<=n/p[j];++j){
            vis[i*p[j]]=1;
            if(i%p[j]==0)break;
            mu[i*p[j]]-=mu[i];
        }
    }
    rep(i,1,n)for(int j=i;j<=n;j+=i)a[j]+=mu[i]*mu[j/i];
}
int main(){
	scanf("%d",&T);
	get_mu(1e6+7);
	while(T--&&~scanf("%d%d",&n,&m)){
		if(n>m)swap(n,m);
		ans=0;
		rep(i,1,n){
			int b=0,c=0;
			for(int j=i;j<=n;j+=i)b+=mu[j];
			for(int j=i;j<=m;j+=i)c+=mu[j];
			ans+=a[i]*b*c;
		}
		printf("%lld\n",ans);
	}
	return 0;
}