Jzoj2756 Longge的问题

做法可以参考这篇：jzoj2581，注意求phi(i)的方法，需要用到sqrt(i)的暴力分解算法

#include<stdio.h>bool vis[40010];int w[20010],t=0;long long phi(int x){long long S=x;for(int i=0;w[i]*w[i]<=x;++i){if(x%w[i]==0)for(S=S/w[i]*(w[i]-1);x%w[i]==0;x/=w[i]);}if(x>1) S=S/x*(x-1);return S;}int main(){for(int i=2;i<=40000;++i){if(!vis[i]) w[t++]=i;for(int j=0;j<t&&i*w[j]<=40000;++j){vis[i*w[j]]=1;if(i%w[j]==0) break;}}int n; long long ans=0; scanf("%d",&n);for(int i=1;i*i<=n;++i)if(n%i==0) ans+=i*phi(n/i)+(n/i)*phi(i);printf("%lld\n",ans);}