hduoj 2824 The Euler function【欧拉函数 打表】

The Euler function

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 6449    Accepted Submission(s): 2720

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
  
  
  
  

   
   
   
   
#include<cstdio>
#include<cstring>
const int maxn = 3000010;
long long phi[maxn];
void Euler(){
	for(int i = 2; i < maxn ; i++){
	 	if(!phi[i]){
	 		for(int j = i; j < maxn; j += i){
	 			if(!phi[j])
	 			    phi[j] = j;
	 			phi[j] = phi[j] / i * (i-1);
			 }
		 }
	}
	for(int i = 3; i < maxn; i++)
	   phi[i] += phi[i-1];
}
int main(){
	int a,b;
    Euler();
	while(~scanf("%d%d",&a,&b)){
		printf("%lld\n",phi[b] - phi[a-1]);
	}
	
	return 0;
}