筛法求欧拉函数（线性）

#include<cstdio>
#include<algorithm>
#include<vector>
#define maxn 10000005
using namespace std;


long long n,phi[maxn];
int siz;
bool vis[maxn];
vector<int>prime;


int main(){
	scanf("%lld",&n);
	
	phi[1]=1;
	for(int i=2;i<=n;i++){
		if(!vis[i]) prime.push_back(i),siz++,phi[i]=i-1;
		for(int j=0;j<siz && i*prime[j]<=n;j++)
		{
			vis[i*prime[j]]=1;
			if(i%prime[j]==0){
				phi[i*prime[j]] = prime[j] * phi[i];
				break;
			}
			else	
				phi[i*prime[j]] = prime[j] * phi[i] - phi[i];
		}
	}
	
	bool flag=0;
	for(int i=1;i<=n;i++)
		printf("%d ",phi[i]);
}