开心的小Q 51Nod - 1742

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 const int maxn = 1e5+10;
 4 int mu[maxn], pri[maxn];
 5 int cnt;
 6 
 7 void init(){
 8     memset(pri, 0, sizeof(pri));
 9     cnt = 0;
10     mu[1] = 1;
11     for(int i = 2; i < maxn; i++){
12         if(!pri[i]) {
13             pri[cnt++] = i;
14             mu[i] = -1;
15         }
16         for(int j = 0; j < cnt; j++){
17             int t = pri[j] * i;
18             if(t > maxn) break;
19             pri[t] = 1;
20             if(i % pri[j] == 0){
21                 mu[t] = 0;
22                 break;
23             } else {
24                 mu[t] = -mu[i];
25             }
26         }
27     }
28 }
29 int F(int n){
30     int ans = n;
31     for(int i = 1; i*i <= n; i++){
32         ans -= mu[i]*(n/(i*i));
33     }
34     return ans;
35 }
36 int solve(int a) {
37     int ans = 0;
38     int L = 1, R = 1;
39     while(L <= a) {
40         ans += (R-L+1)*F(a/L);
41         if(R >= a) break;
42         L = R+1;
43         R = a/(a/L);
44     }
45     return ans;
46 }
47 
48 int main(){
49     int a,b;
50     init();
51     while(scanf("%d %d", &a, &b) != EOF){
52         printf("%d\n", solve(b) - solve(a-1));
53     }
54 }