#include <iostream>
using namespace std;
using ll = long long int;
ll dp[5010], cnt[5010], MOD = 1000000007;
int main() {
    int N; cin >> N; dp[0] = 1;
    for(int i=0; i<N; i++) {
        int val; cin >> val;
        cnt[val]++;
    }
    for(int i=0; i<N; i++) {
        for(int k=i; k>=0; k--) {
            (dp[k+1] += dp[k] * cnt[i]) %= MOD;
        }
    }
    ll fact = 1, ans = 0, cnt = 0;
    for(int i=N; i>=0; i--) {
        ll val = dp[i] * fact % MOD;
        if(i % 2 == 0) ans = (ans + val      ) % MOD;
        else           ans = (ans - val + MOD) % MOD;
        (fact *= (++cnt)) %= MOD;
    }
    cout << ans << endl;
    return 0;
}