#include<iostream>
#include<algorithm>
#include<stack>
#include<vector>
#include<set>
#include<string>
#include<cstdint>

using namespace std;
using ll = long long;

#include<atcoder/modint>
using mint = atcoder::modint1000000007;

mint fac[1<<17],ifac[1<<17];
int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    
    int n;
    cin>>n;
    vector<int> x(n);
    int sum = 0;
    for(int i = 0;i<n;i++){
        cin>>x[i];
        sum += x[i];
    }
    if(sum==1){
        cout<<1<<endl;
        return 0;
    }

    mint ans = sum;
    for(int i = 0;i<n;i++){
        mint tmp = sum * (sum-1);
        ans -= mint(sum-1) * mint(x[i]*(x[i]-1)) / tmp;
    }
    cout<<ans.val()<<endl;
    
}