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

 

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欧拉函数....

代码：

#include<stdio.h>
#include<string.h>
const int maxn=3000001;
__int64 phi[maxn];
int main()
{
    int st,en,i,j;
        for(i=1;i<maxn;i++)
            phi[i]=i;
        for(i=2;i<maxn;i+=2)
            phi[i]/=2;
        for(i=3;i<maxn;i+=2)
        {
            if(phi[i]==i)
            {
                for(j=i;j<maxn;j+=i)
                {
                    phi[j]=phi[j]/i*(i-1);      /*from left to right*/
                }
            }
        }
    while(scanf("%d%d",&st,&en)!=EOF)
    {
    
        __int64 ans=0;
        for(i=st;i<=en;i++)
        {
            ans+=phi[i];
        }
        printf("%I64d
",ans);
    }

    return 0;
}