线筛欧拉函数

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

题解

注意内存限制

#include
#define MAX_N 3000100
long long phi[MAX_N];

void Eular(){
    for(int i=1;ifor(int i=2;iif(phi[i]==i)
            for(int k=i;k1);
            }
        phi[i]+=phi[i-1];
    }
}

int main()
{
    Eular();
    int a,b;
    while(scanf("%d%d",&a,&b)!=EOF){
        printf("%lld\n",phi[b]-phi[a-1]);
    }
    return 0;
}

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