#include <bits/stdc++.h>
using namespace std;
#include <atcoder/modint>
using namespace atcoder;
//using mint = modint998244353;
using mint = modint1000000007;
using ll = long long;
using ld = long double;
using pll = pair<ll, ll>;
using tlll = tuple<ll, ll, ll>;
constexpr ll INF = 1LL << 60;
template<class T> bool chmin(T& a, T b) {if (a > b) {a = b; return true;} return false;}
template<class T> bool chmax(T& a, T b) {if (a < b) {a = b; return true;} return false;}
ll safemod(ll A, ll M) {return (A % M + M) % M;}
ll divfloor(ll A, ll B) {if (B < 0) {return divfloor(-A, -B);} return (A - safemod(A, B)) / B;}
ll divceil(ll A, ll B) {if (B < 0) {return divceil(-A, -B);} return divfloor(A + B - 1, B);}
template<class T> void unique(vector<T> &V) {V.erase(unique(V.begin(), V.end()), V.end());}
template<class T> void sortunique(vector<T> &V) {sort(V.begin(), V.end()); V.erase(unique(V.begin(), V.end()), V.end());}
#define FINALANS(A) do {cout << (A) << '\n'; exit(0);} while (false)
template<class T> void printvec(vector<T> &V) {int _n = V.size(); for (int i = 0; i < _n; i++) cout << V[i] << (i == _n - 1 ? '\n' : ' ');}
template<class T> void printvect(vector<T> &V) {for (auto v : V) cout << v << '\n';}
template<class T> void printvec2(vector<vector<T>> &V) {for (auto &v : V) printvec(v);}

int main()
{
  ll N;
  cin >> N;
  vector<ll> A(N);
  for (ll i = 0; i < N; i++)
  {
    cin >> A.at(i);
  }

  vector<ll> cnt(N, 0);
  for (auto a : A)
  {
    if (a < N)
      cnt.at(a)++;
  }

  vector dp(2, vector(N + 1, mint(0)));
  dp.at(0).at(0) = 1;
  for (ll i = 0; i < N; i++)
  {
    ll pi = i % 2, ni = 1 - pi;

    for (ll j = 0; j <= N; j++)
    {
      dp.at(ni).at(j) = 0;
    }

    for (ll j = 0; j < N; j++)
    {
      dp.at(ni).at(j + 1) += cnt.at(i) * dp.at(pi).at(j);
      dp.at(ni).at(j) += dp.at(pi).at(j);
    }
  }

  vector<mint> fac(N + 1);
  fac.at(0) = 1;
  for (ll i = 1; i <= N; i++)
  {
    fac.at(i) = fac.at(i - 1) * i;
  }

  mint ans = 0;
  for (ll j = 0; j <= N; j++)
  {
    mint tmp = (j % 2 == 0 ? 1 : -1) * dp.at(N % 2).at(j) * fac.at(N - j);
    ans += tmp;
  }
  cout << ans.val() << endl;
}