#include <bits/stdc++.h>
#pragma pack(1)
#pragma GCC target("avx,avx2")
#pragma GCC optimization("O3")
#pragma GCC optimization("unroll-loops")
using namespace std;
long long int fact(long long int n) {
  if (n == 0) return 1;
  return n * fact(n - 1) % 998244353;
}
long long int gcdExtended(long long int a, long long int b, long long int *x,
                          long long int *y);
long long int modInverse(long long int b, long long int m) {
  long long int x, y;
  long long int g = gcdExtended(b, m, &x, &y);
  if (g != 1) return -1;
  return (x % m + m) % m;
}
long long int modDivide(long long int a, long long int b, long long int m) {
  a = a % m;
  long long int inv = modInverse(b, m);
  return (inv * a) % m;
}
long long int gcdExtended(long long int a, long long int b, long long int *x,
                          long long int *y) {
  if (a == 0) {
    *x = 0, *y = 1;
    return b;
  }
  long long int x1, y1;
  long long int gcd = gcdExtended(b % a, a, &x1, &y1);
  *x = y1 - (b / a) * x1;
  *y = x1;
  return gcd;
}
int main() {
  long long int t;
  cin >> t;
  while (t--) {
    long long int n;
    cin >> n;
    long long int a[n];
    for (long long int i = 0; i < n; ++i) cin >> a[i];
    sort(a, a + n);
    long long int cmax = 0;
    long long int csecmax = 0;
    long long int x = a[n - 1];
    for (long long int i = n - 1; i >= 0; --i) {
      if (a[i] != a[n - 1]) {
        x = a[i];
        break;
      }
    }
    for (long long int i = 0; i < n; ++i) {
      if (a[i] == a[n - 1])
        ++cmax;
      else if (a[i] == x)
        ++csecmax;
    }
    if (cmax > 1) {
      cout << fact(n) << endl;
    } else if ((a[n - 1] - x) > 1) {
      cout << "0" << endl;
    } else {
      long long int ans = 1;
      for (long long int i = csecmax + 1; i <= csecmax + cmax; ++i) {
        ans = ans * i % 998244353;
      }
      long long int fin =
          ((ans % 998244353) - (1 % 998244353) + 998244353) % 998244353;
      long long int z = ((fact(n) % 998244353) * (fin % 998244353)) % 998244353;
      cout << modDivide(z, ans, 998244353) << endl;
    }
  }
  return 0;
}
