#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'; }