51nod 1225 数学

 1 #include <bits/stdc++.h>
 2 #define ll  __int64
 3 using namespace  std;
 4 ll mod=1000000007;
 5 ll ni=0;
 6 ll pow(ll a,ll b)
 7 {
 8     ll re=1;
 9     while(b)
10     {
11         if(b&1)
12             re=(re*a)%mod;
13         b>>=1;
14         a=(a*a)%mod;
15     }
16     return re;
17 }
18 ll sum(ll l,ll r)
19 {
20     return ((l+r)%mod)*((r-l+1)%mod)%mod*ni%mod;
21 }
22 int  main()
23 {
24      ni=pow(2ll,mod-2);
25     ll n,r,ans=0;
26     scanf("%I64d",&n);
27     for(int ll i=1;i<=n;i=r+1){
28         r=n/(n/i);
29         ans=(ans+(n/i)%mod*sum(i,r)%mod)%mod;
30     }
31     n%=mod;
32     printf("%I64d\n",(n*n%mod-ans+mod)%mod);
33     return 0;
34 }