#include <bits/stdc++.h>
using namespace std;
#define pb push_back
using ll = long long;
using vi = vector <int>;
const ll mod = 1e9 + 7;

ll qpow(ll a, ll b) {
	ll r = 1, t = a;
	for(; b; b /= 2) {
		if(b & 1)
			r = r * t % mod;
		t = t * t % mod;
	}
	return r;
}

const int N = 1e5 + 11;
int a[N];

int main() {
	ios::sync_with_stdio(0);
	
	int n; cin >> n;
	for(int i = 0; i < n; i ++)
		cin >> a[i];
		
	int s = accumulate(a, a + n, 0);
	
	ll ans = 0;
	for(int i = 0; i < n; i ++) {
		ans += a[i] * qpow(s, mod - 2) % mod
			* (a[i] - 1) % mod * qpow(s - 1, mod - 2);
		
		ans %= mod;
	}
	
	ans = s - ans * (s - 1);
	ans %= mod;
	if(ans < 0) ans += mod;
	cout << ans << '\n';
}