HDUOJ-----2824The Euler function

 1 #include<stdio.h>
 2 #include<string.h>
 3 const int maxn=3000001;
 4 __int64 phi[maxn];
 5 int main()
 6 {
 7     int st,en,i,j;
 8         for(i=1;i<maxn;i++)
 9             phi[i]=i;
10         for(i=2;i<maxn;i+=2)
11             phi[i]/=2;
12         for(i=3;i<maxn;i+=2)
13         {
14             if(phi[i]==i)
15             {
16                 for(j=i;j<maxn;j+=i)
17                 {
18                     phi[j]=phi[j]/i*(i-1);      /*from left to right*/
19                 }
20             }
21         }
22     while(scanf("%d%d",&st,&en)!=EOF)
23     {
24     
25         __int64 ans=0;
26         for(i=st;i<=en;i++)
27         {
28             ans+=phi[i];
29         }
30         printf("%I64d\n",ans);
31     }
32 
33     return 0;
34 }