#include using namespace std; using ll = long long; constexpr char newl = '\n'; constexpr int MAXN = 5000; // https://noshi91.hatenablog.com/entry/2019/03/31/174006 template struct ModInt { using u64 = std::uint_fast64_t; static constexpr u64 MOD = Modulus; u64 val; constexpr ModInt(const u64 x = 0) noexcept : val(x % MOD) {} constexpr ModInt operator+() const noexcept { return ModInt(*this); } constexpr ModInt operator-() const noexcept { ModInt res(*this); if (res.val != 0) res.val = MOD - res.val; return res; } constexpr bool operator==(const ModInt& rhs) const noexcept { return val == rhs.val; } constexpr bool operator!=(const ModInt& rhs) const noexcept { return val != rhs.val; } // prefix increment/decrement constexpr ModInt& operator++() noexcept { return *this += ModInt(1); } constexpr ModInt& operator--() noexcept { return *this -= ModInt(1); } // postfix increment/decrement constexpr ModInt operator++(int) noexcept { ModInt tmp(*this); ++*this; return tmp; } constexpr ModInt operator--(int) noexcept { ModInt tmp(*this); --*this; return tmp; } constexpr ModInt operator+(const ModInt& rhs) const noexcept { return ModInt(*this) += rhs; } constexpr ModInt operator-(const ModInt& rhs) const noexcept { return ModInt(*this) -= rhs; } constexpr ModInt operator*(const ModInt& rhs) const noexcept { return ModInt(*this) *= rhs; } constexpr ModInt operator/(const ModInt& rhs) const noexcept { return ModInt(*this) /= rhs; } constexpr ModInt& operator+=(const ModInt& rhs) noexcept { val += rhs.val; if (val >= MOD) val -= MOD; return *this; } constexpr ModInt& operator-=(const ModInt& rhs) noexcept { if (val < rhs.val) val += MOD; val -= rhs.val; return *this; } constexpr ModInt& operator*=(const ModInt& rhs) noexcept { val = val * rhs.val % MOD; return *this; } // prime Modulus only constexpr ModInt& operator/=(const ModInt& rhs) noexcept { return *this *= rhs.inv(); } // prime Modulus only constexpr ModInt inv() const noexcept { return pow(*this, MOD - 2); } }; template constexpr ModInt pow(ModInt x, std::uint_fast64_t n) { ModInt res(1); while (n) { if (n & 1) res *= x; x *= x; n >>= 1; } return res; } template istream& operator>>(istream& is, ModInt& x) { std::uint_fast64_t val; is >> val; x = ModInt(val); return is; } template ostream& operator<<(ostream& os, const ModInt& x) { return os << x.val; } using mint = ModInt<1000000007>; // g++ -Wl,--stack,[STACK SIZE] [file] でスタックサイズを増やすか、 // グローバル変数として宣言して使うこと!!! template struct Comb { array fact, fact_inv; constexpr Comb() noexcept { fact[0] = 1; for (size_t i = 1; i <= MAXV; i++) { fact[i] = fact[i - 1] * i; } fact_inv[MAXV] = fact[MAXV].inv(); for (size_t i = MAXV; i > 0; i--) { fact_inv[i - 1] = fact_inv[i] * i; } } constexpr T operator()(int n, int k) const noexcept { if (n < k || n < 0 || k < 0) return 0; return fact[n] * fact_inv[k] * fact_inv[n - k]; } constexpr T perm(int n, int k) const noexcept { if (n < k || n < 0 || k < 0) return 0; return fact[n] * fact_inv[n - k]; } }; const Comb<200000> comb; int main() { cin.tie(nullptr); ios::sync_with_stdio(false); int n; cin >> n; array cnt{}; for (int i = 0; i < n; i++) { int a; cin >> a; ++cnt[a]; } vector dp(n + 1, 0); dp[0] = 1; for (int i = 0; i < n; i++) { if (!cnt[i]) continue; for (int j = i; j >= 0; j--) { dp[j + 1] += dp[j] * cnt[i]; } } mint ans = 0; for (int i = 0; i <= n; i++) { if (dp[i] == 0) continue; mint tmp = comb.fact[n - i] * dp[i]; if (i & 1) ans -= tmp; else ans += tmp; } cout << ans << newl; return 0; }