HDU 5597 GTW likes function 欧拉函数

题目链接：

http://acm.hdu.edu.cn/showproblem.php?pid=5597

题意：

http://bestcoder.hdu.edu.cn/contests/contest_chineseproblem.php?cid=658&pid=1003

题解：

f0(1)=2;  f0(2)=3;  f0(3)=4;

f1(1)=3;  f1(2)=4;  f1(3)=5;

f2(1)=4;  ......

所以归纳出：fn(x)=n+x+1;  orz

然后求euler(n+x+1).

代码：

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
typedef long long LL;

LL euler_phi(LL x) {
    LL ret = x;
    for (LL i = 2; i*i <= x; i++) {
        if (x%i == 0) {
            ret = ret / i*(i - 1);
            while (x%i == 0) x /= i;
        }
    }
    if (x > 1) ret = ret / x*(x - 1);
    return ret;
}

int main() {
    LL n, x;
    while (scanf("%lld%lld", &n, &x) == 2 && n) {
        printf("%lld\n", euler_phi(n + x + 1));
    }
    return 0;
}