HDUOJ-----2824The Euler function

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

 

 

Recommend

 

欧拉函数....

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("%I64d\n",ans);

31     }

32 

33     return 0;

34 }

View Code