#include<iostream>
#include<cstring>
#include<vector>
#include<algorithm>
using namespace std;
using LL = long long;

int main(){

#ifdef LOCAL
    freopen("data.in", "r", stdin);
    freopen("data.out", "w", stdout);
#endif

    cin.tie(0);
    cout.tie(0);
    ios::sync_with_stdio(0);

    int T;
    cin >> T;
    while(T--){
        int n;
        cin >> n;
        vector<int> a(n + 1), cnt(n + 1);
        for(int i = 1; i <= n; i++){
            cin >> a[i];
            cnt[a[i]] += 1;
        }
        int mx1 = 0, mx2 = 0;
        for(int i = 1; i <= n; i++){
            if (cnt[i] >= mx1){
                mx2 = mx1;
                mx1 = cnt[i];
            }
            else if (cnt[i] > mx2){
                mx2 = cnt[i];
            }
        }

        auto solve = [&](int x, int y){
            int ans = max({x, y, x ^ y});
            if (x != 0){
                for(int i = 1; i <= __lg(x); i++){
                    if (x >> i & 1){
                        int t = (x ^ (1 << i)) | ((1 << i) - 1);
                        ans = max(ans, t ^ y);
                    }
                }
            }
            return ans;
        };

        cout << max(solve(mx1, mx2), solve(mx2, mx1)) << '\n';
    }

}