HDU 2824 The Euler function

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)

欧拉函数模板题。
注意开long long。
丧心病狂卡内存。

#include<cstdio>
#include<cstring>
const int n=3000000;
long long f[n+5];
void make()
{
    int i,j,k,x,y,z;
    f[1]=1;
    for (i=2;i<=n;i++)
      if (!f[i])
        for (j=i;j<=n;j+=i)
        {
          if (!f[j]) f[j]=j;
          f[j]=f[j]/i*(i-1);
        }
    for (i=1;i<=n;i++)
      f[i]+=f[i-1];
}
int main()
{
    int x,y;
    make();
    while (scanf("%d%d",&x,&y)==2)
      printf("%lld\n",f[y]-f[x-1]);
}