[hdu]2848 the Euler function[Euler function] [water problem]

Problem Description
The Euler function phi is an important kind of function in number theory, (n) represents the amount of the numbers which a Re smaller than N and coprime to n, and this function have a lot of beautiful characteristics. Here comes a very easy question:suppose is given a, B, try to calculate (a) + (a+1) +....+ (b)

Input
There is several test cases. Each line has a integers a, B (2

#include <stdio.h>
#define MAX_N 3000100
int phi[max_n];

void Init () {for
    (int i=1;i<max_n;i++) phi[i]=i;
    for (int i=2;i<max_n;i++)
        if (phi[i]==i) for
            (int j=i;j<max_n;j+=i)
                phi[j]=phi[j]/i* (i-1);
}

int main ()
{
    init (); int a, b;
    while (~SCANF ("%d%d", &a,&b)) {
        long long ans=0;
        for (int i=a;i<=b;i++)
            ans+=phi[i];
        printf ("%lld\n", ans);
    }
    return 0;
}