#include <bits/stdc++.h>
using namespace std;
[[maybe_unused]] const int MOD = 1000000007;
[[maybe_unused]] const int INTMAX = numeric_limits<int>::max();
void writeln() { cout << "\n"; }
template <class T>
inline void print(T&& a);
template <class T>
inline void priws(T&& a);
template <class T>
inline void read(T& a);
template <class... Args>
inline void readln(Args&... args) {
  (read(args), ...);
}
template <class H, class... T>
inline void writeln(H&& h, T&&... t) {
  priws(h);
  (print(t), ...);
  writeln();
}
void run() {
  int m = 27;
  int n;
  readln(n);
  vector<int> a(n);
  readln(a);
  vector<vector<int>> c(n + 1, vector<int>(m, 0));
  vector<vector<int>> d(n + 1, vector<int>(m, 0));
  vector<vector<int>> counts(m + 1, vector<int>(n + 1, n));
  for (int i = 0; i < (int)(n); ++i) c[i + 1] = c[i], c[i + 1][a[i]]++;
  for (int i = n - 1; i >= (int)(0); --i)
    d[i] = d[i + 1], counts[a[i]][++d[i][a[i]]] = i;
  int ans = 0;
  for (int left = 0; left < (int)(n); ++left)
    for (int j = 1; j < (int)(m); ++j)
      if (int x = c[left][j], right = counts[j][x]; right > left) {
        int temp = 0;
        for (int k = 1; k < (int)(m); ++k)
          temp = max(temp, c[right][k] - c[left][k]);
        ans = max(ans, x * 2 + temp);
      }
  writeln(ans);
}
int main() {
  ios_base::sync_with_stdio(false);
  int t;
  readln(t);
  for (int i = 0; i < (int)(t); ++i) run();
  cerr << fixed << setprecision(0)
       << "Execution time = " << 1000.0 * clock() / CLOCKS_PER_SEC << "ms\n";
  return 0;
}
template <class T1, class T2>
inline ostream& operator<<(ostream& os, pair<T1, T2> const& _a);
template <
    typename T, typename D = decltype(*begin(declval<T>())),
    typename enable_if<!is_same<T, basic_string<char>>::value>::type* = nullptr>
ostream& operator<<(ostream& os, T const& _a) {
  auto it = begin(_a);
  if (it != end(_a)) os << *it++;
  while (it != end(_a))
    os << "\n "[is_fundamental<typename T::value_type>::value] << *it++;
  return os;
}
template <class T1, class T2>
inline ostream& operator<<(ostream& os, pair<T1, T2> const& _a) {
  return os << _a.first << " " << _a.second;
}
template <class T1, class T2>
inline istream& operator>>(istream& is, pair<T1, T2>& _a) {
  return is >> _a.first >> _a.second;
}
template <class T>
inline istream& operator>>(istream& is, vector<T>& _a) {
  for (int i = 0; i < (int)(_a.size()); ++i) is >> _a[i];
  return is;
}
template <class T>
inline void print(T&& _a) {
  cout << " " << _a;
}
template <class T>
inline void priws(T&& _a) {
  cout << _a;
}
template <class T>
inline void read(T& _a) {
  cin >> _a;
}
