#include <bits/stdc++.h>
using namespace std;
const int N = 100005, P = 1e9 + 7;
int n, s, ans, c[N], f[N];
inline int pw(int a, int b) {
  int r = 1;
  for (; b; b >>= 1, a = 1ll * a * a % P)
    if (b & 1) r = 1ll * r * a % P;
  return r;
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) scanf("%d", &c[i]), s += c[i];
  f[1] = 1ll * (s - 1) * (s - 1) % P * pw(s, P - 2) % P;
  for (int i = 1; i < 100000; i++)
    f[i + 1] = ((2 * f[i] % P - f[i - 1] + P) % P -
                1ll * (s - 1) * pw(s - i, P - 2) % P + P) %
               P;
  for (int i = 1; i <= n; i++) ans = (ans + f[c[i]]) % P;
  printf("%d\n", ans);
  return 0;
}
