hdu 2824 The Euler function (欧拉函数)

The Euler function

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 3333    Accepted Submission(s): 1368

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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求欧拉函数，打表题：

 

//453MS    23700K    484 B    G++
#include<stdio.h>
#define N 3000005
__int64 ans[N];
void init()
{
    for(int i=1;i<N;i++) ans[i]=i;
    for(int i=2;i<N;i+=2) ans[i]/=2;
    for(int i=3;i<N;i+=2) 
        if(ans[i]==i){
            for(int j=i;j<N;j+=i) ans[j]=ans[j]/i*(i-1);
        }
}
int main(void)
{
    int a,b;
    init();
    while(scanf("%d%d",&a,&b)!=EOF)
    {
        __int64 ret=0;
        for(int i=a;i<=b;i++) ret+=ans[i];
        printf("%I64d
",ret);
    }
    return 0;
}