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): 4482 Accepted Submission(s): 1859



[align=left]Problem Description[/align]
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)

[align=left]Input[/align]
There are several test cases. Each line has two integers a, b (2<a<b<3000000).

[align=left]Output[/align]
Output the result of (a)+ (a+1)+....+ (b)

[align=left]Sample Input[/align]

3 100

[align=left]Sample Output[/align]

3042
#include <iostream>
#include <cstdio>
using namespace std;
const int N=3000000+10;
long long phi
;
inline void Init(){
long long i,j;
phi[0]=0;
for(i=1;i<N;i++)  phi[i]=i;
for(i=2;i<N;i+=2)  phi[i]/=2;
for(i=3;i<N;i+=2)
if(phi[i]==i){
for(j=i;j<N;j+=i)
phi[j]=phi[j]/i*(i-1);
}
}
int main(){
Init();
int a,b,i;
long long sum;
while(cin>>a>>b){
sum=0;
for(i=a;i<=b;i++)
sum+=phi[i];
cout<<sum<<endl;
}
return 0;
}