我与我的厌氧代码

#include<bits/stdc++.h>
#define int long long
using namespace std;
inline int read(){
	int x=0;bool f=1;char c=getchar();
	for(;!isdigit(c);c=getchar())if(c=='-')f=0;
	for(;isdigit(c);c=getchar())x=(x<<3)+(x<<1)+c-'0';
	return f?x:(~(x-1));
}
int n,N;
namespace Sub1{
	#define n N
	int a[4560],ans;
	inline int gcd(int a,int b){
		if(a<b)swap(a,b);
		return (!b)?a:gcd(b,a%b);
	}
	signed work(){
		for(int i=1;i<=n;++i)a[i]=read();
		for(int i=1;i<=n;++i)
			for(int j=1;j<=n;++j)
				ans+=a[i]*a[j]/gcd(a[i],a[j]);
		printf("%lld",ans);
	}
	#undef n
}
namespace Sub2{
	int CNT[50010],g[50010],s[50010];
	bool notprime[50010];
	int prime[10000],cnt,mu[50010],ANS;
	inline void getprime(int LIM){
		notprime[1]=1,mu[1]=1;
		for(int i=2;i<=LIM;++i){
			if(!notprime[i])prime[++cnt]=i,mu[i]=-1;
			for(int j=1;j<=cnt&&i*prime[j]<=LIM;++j){
				notprime[i*prime[j]]=1;
				if(!(i%prime[j])){
					mu[i*prime[j]]=0;
					break;
				}
				mu[i*prime[j]]=mu[i]*mu[prime[j]];
			}
		}
	} 
	signed work(){
		for(int i=1,a;i<=N;++i){
			CNT[a=read()]++;
			n=max(n,a);
		}
		for(int i=1,res=0;i<=n;++i,res=0){
			for(int j=1;j<=n/i;++j)
				res+=CNT[j*i]*j;
			g[i]=res*res;
		}
		getprime(50000);
		for(int i=1;i<=n;++i)
			for(int j=1;j<=n/i;++j)
				s[i*j]+=mu[i]*i;
		for(int i=1;i<=n;++i)ANS+=s[i]*g[i]*i;
		cout<<ANS;
	}
}
signed main(){
	N=read();
	if(N<=4500)Sub1::work();
	else Sub2::work();
}