POJ 2407 Relatives

Description

Given n, a positive integer, how many positive integers less than n are relatively prime to n? Two integers a and b are relatively prime if there are no integers x > 1, y > 0, z > 0 such that a = xy and b = xz.

Input

There are several test cases. For each test case, standard input contains a line with n <= 1,000,000,000. A line containing 0 follows the last case.

Output

For each test case there should be single line of output answering the question posed above.

Sample Input
7
12
0

Sample Output
6
4

欧拉函数裸题。

#include<iostream>#include<cstdio>#include<cmath>using namespace std;int n;int phi(int x){    int ans=x,tp=sqrt(1.0*x);    for(int i=2;i<=tp;i++)        if(x%i==0)        {            ans-=ans/i;            while(x%i==0)                x/=i;        }    if(x>1)        ans-=ans/x;    return ans;}int main(){    while(scanf("%d",&n)&&n)        printf("%d\n",phi(n));    return 0;}