欧拉函数

codevs4415

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
using namespace std;
#define LL long long 
LL a,b,c,n;
LL phi(LL x)//求单个欧拉函数的算法
{
	LL t=x;
	for (LL i=2;i*i<=x;i++)  //注意i*i<=x的表示
	  if (x % i==0)
	  {
		  t=t/i*(i-1);
		  while (x %i ==0) x/=i;
	  }
	if (x>1) t=t/x*(x-1);//这句保证最后的质数被算到
	return t;
}
LL sumphi(LL x)
{
	LL ans=0;
	for (LL i=1;i*i<=x;i++)
	   if (x % i==0) 
	   {
		   ans+=phi(i);
		   if (i*i<x) ans+=phi(x / i);
	   }
	return ans;
}
LL sumgcd()
{
	LL ans=0;
	for (LL i=1;i*i<=n;i++)
		if (n %i ==0) 
		{
			ans+=(LL)i*phi(n/i);
			if (i*i<n) ans+=(LL)(n/i)*phi(i);
		}
	return ans;
}
int main()
{
	scanf("%lld", &n);
	a=phi(n);
	b=sumgcd();
	c=sumphi(n);
	printf("%lld", a+b % c);
	system("pause");
    return 0;
}

欧拉函数