#include <bits/stdc++.h>
using namespace std;
const long long p = 1e9 + 7;
int n, a[2505], mx, s, ch, ans;
long long f[100005];
long long ksm(long long x, int y) {
  long long sun = 1;
  while (y) {
    if (y & 1) sun = sun * x % p;
    y >>= 1;
    x = x * x % p;
  }
  return sun;
}
int main() {
  cin >> n;
  for (int i = 1; i <= n; i++)
    scanf("%d", &a[i]), mx = max(a[i], mx), s += a[i];
  f[1] = ksm(s - 1, 2) * ksm(s, p - 2) % p;
  ch = f[1];
  for (int i = 2; i <= mx; i++) {
    ch = (ch - ksm(s - i + 1, p - 2) * (s - 1) % p + p) % p;
    f[i] = (f[i - 1] + ch) % p;
  }
  for (int i = 1; i <= n; i++) ans = (ans + f[a[i]]) % p;
  cout << ans;
}
