题目链接:http://61.187.179.132/JudgeOnline/problem.php?id=2956
题意:给出n和m。计算:
思路:
i64 n,m;
i64 cal(i64 m,i64 n)
{
i64 ans=0,i,x,y;
for(i=1;i<=n;i++)
{
x=m/i; y=min(n,m/x);
ans+=(i+y)*(y-i+1)/2%mod*x%mod;
ans%=mod;
i=y;
}
return ans;
}
i64 get(i64 n)
{
i64 a=n,b=n+1,c=2*n+1;
if(a%2==0) a>>=1;
else b>>=1;
if(a%3==0) a/=3;
else if(b%3==0) b/=3;
else c/=3;
return a*b%mod*c%mod;
}
i64 cal(i64 n,i64 m,i64 k)
{
i64 ans=0,i,x,y,z;
for(i=1;i<=k;i++)
{
x=n/i; y=m/i; z=min(k,min(n/x,m/y));
ans+=(get(z)-get(i-1))%mod*x%mod*y%mod;
ans%=mod;
i=z;
}
return ans;
}
int main()
{
RD(n,m);
if(n>m) swap(n,m);
i64 ans1=(n*n%mod-cal(n,n))%mod*(m*m%mod-cal(m,m))%mod;
i64 ans2=n*n%mod*m%mod-n*cal(m,n)%mod-m*cal(n,n)%mod+cal(n,m,n)%mod;
i64 ans=(ans1-ans2)%mod;
if(ans<0) ans+=mod;
PR(ans);
}