题目链接：https://www.51nod.com/onlineJudge/questionCode.html#!problemId=1136

思路：欧拉函数求小于或等于n且与n互质的数字的个数

代码：

1 #include 
         
           2 #include 
          
            3 using namespace std; 4  5 int euler(int n){ 6     int cnt = n; 7     for(int i = 2;i <= sqrt(n);i ++){ 8         if(n%i == 0){ 9             cnt = cnt/i*(i-1);10             while(n%i == 0)11                 n /= i;12         }13     }14     if(n > 1)    cnt = cnt/n*(n-1);15     return cnt;16 }17 int main()18 {19     int n;20     while(cin>>n){21         int res = euler(n);22         cout<
           
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