#include <bits/stdc++.h>

typedef long long LL;

const int N = 5000 + 7;
const int MOD = 1e9 + 7;

int n, fac[N], f[N], a[N];

int main() {

  scanf("%d", &n);
  for(int i = 1, x; i <= n; ++i) {
    scanf("%d", &x);
    ++a[x + 1];
  }

  fac[0] = 1;
  for(int i = 1; i <= n; ++i)
    fac[i] = 1LL * fac[i - 1] * i % MOD;

  f[0] = 1;
  for(int i = 1; i <= n; ++i)
    for(int j = i; j >= 1; --j)
      f[j] = (f[j] + 1LL * f[j - 1] * a[i]) % MOD;

  int ans = 0;
  for(int i = 0; i <= n; ++i)
    ans = (ans + (i & 1 ? -1LL : 1LL) * f[i] * fac[n - i]) % MOD;
  
  printf("%d\n", (ans + MOD) % MOD);
  
  return 0;

}