线性欧拉筛+素数筛

Euler+Prime.cpp

#include <cstdio>
using namespace std;
const int maxn=1e7+7;
int prime[maxn],phi[maxn],n,totprime;
int main()
{
	scanf("%lld",&n);
	phi[1]=1;
	for (int i=2;i<=n;i++)
	{
		if (!phi[i])
		{
			prime[totprime++]=i;
			phi[i]=i-1;
		}
		for (int j=0;j<totprime&&i*prime[j]<=n;j++)
		{
			if (i%prime[j])
				phi[i*prime[j]]=phi[i]*(prime[j]-1);
			else
			{
				phi[i*prime[j]]=phi[i]*prime[j];
				break;
			}
		}
	}
	return 0;
}