歐拉函數板子

bool book[N];  
int prime[N],euler[N];  
int res;  
void  eratosthenes_sieve()  
{  
    res=0;  
    memset(book,false,sizeof(book));  
     for(int i=2;i<maxn;i++)  
    {  
      if(!book[i])  
          prime[res++]=i,euler[i]=i-1;  
         
      for(int j=0;j<res&&i*prime[j]<maxn;j++)  
      {  
          if(i%prime[j]==0)  
          {  
              euler[i*prime[j]]=euler[i]*prime[j];  
              break;  
          }  
          euler[i*prime[j]]=euler[i]*(prime[j]-1);  
      }  
}