The Euler function

Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others) Total Submission(s): 3284 Accepted Submission(s): 1350

Problem Description

The Euler function phi is an important kind of function in number theory, (n) represents the amount of the numbers which are smaller than n and coprime to n, and this function has a lot of beautiful characteristics. Here comes a very easy question: suppose you are given a, b, try to calculate (a)+ (a+1)+....+ (b)

Input

There are several test cases. Each line has two integers a, b (2<a<b<3000000).

Output

Output the result of (a)+ (a+1)+....+ (b)

Sample Input

3 100

Sample Output

3042

Source

2009 Multi-University Training Contest 1 - Host by TJU

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代码：

 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("%I64dn",ans);
31     }
32 
33     return 0;
34 }

HDUOJ-----2824The Euler function

The Euler function