Answer is here!

#include <bits/stdc++.h> 

using namespace std;

typedef long long ll;

const int MAXN = 5e5 + 10;
const int mod = 20051131;

int n, cnt[MAXN]; ll ans = 1, sum;

int main() {
    scanf("%d", &n);
    for (int i = 1, x; i <= n; i++) scanf("%d", &x), cnt[x]++;
    sort(cnt + 1, cnt + n + 1, greater<int>());
    for (int i = 1; i <= n; i++) {
        if (!cnt[i]) break;
        for (int j = 1; j < cnt[i]; j++) ans = ans * j % mod;
        if (i > 1) ans = ans * (sum - (ll)(i - 1) * cnt[i]) % mod; sum += cnt[i];
    }
    printf("%lld", ans);
}

Thank you very much!