#include<iostream>
#include<cstdio>
#include<algorithm>
#include<string>
#include<cstring>
#include<cmath>
#include<set>
#include<map>
#include<vector>
#include<queue>
#include<unordered_map>
#include<stack>
using namespace std;
//#define int long long
#define scanf scanf_s
typedef pair<int, int> PII;
const int mod = 1000000007;
const int INF = 0x3f3f3f3f3f3f3f3f;
const double ef = 1e-12;

#define rep(i,a, b) for(int i = a;i<=b;i++)
#define pre(i,a, b) for(int i = a;i>=b;i--)


using LL = long long;
using ll = long long;
const int N = 200005;

#define pb push_back
#define sc(x) scanf("%d",&x)

int cnt[N];

int hz[35];

int get(int x, int y)
{
    int res = 0;
    pre(i, 20, 0)
    {
        int u = 0, v = 0;
        if (x >> i & 1) u = 1;
        if (y >> i & 1) v = 1;
        if (u == 0 && v == 0) continue;
        if (u == v && u == 1)
        {
            res |= hz[i];
            return res;
        }
        else
        {
            res |= (1 << i);
        }
    }
    return res;
}

void solve()
{
    int n;
    sc(n);
    rep(i, 1, n) cnt[i] = 0;
    rep(i, 1, n) {
        int x; sc(x); cnt[x]++;
    }
    int mx = 0, cmx = 0;
    sort(cnt + 1, cnt + n + 1);
    mx = cnt[n];
    cmx = cnt[n - 1];
    if (cmx == 0) printf("%d\n", mx);
    else printf("%d\n", get(mx, cmx));
}


int main() {

    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    hz[0] = 1;
    rep(i, 1, 20) {
        hz[i] = (hz[i - 1] | (1 << i));
    }
    int t = 1;
    cin >> t;
    while (t--) {
        solve();
    }
    return 0;
}

answer.code:18:17: warning: overflow in conversion from ‘long int’ to ‘int’ changes value from ‘4557430888798830399’ to ‘1061109567’ [-Woverflow]
   18 | const int INF = 0x3f3f3f3f3f3f3f3f;
      |                 ^~~~~~~~~~~~~~~~~~
answer.code: In function ‘void solve()’:
answer.code:15:15: error: ‘scanf_s’ was not declared in this scope; did you mean ‘scanf’?
   15 | #define scanf scanf_s
      |               ^~~~~~~
answer.code:30:15: note: in expansion of macro ‘scanf’
   30 | #define sc(x) scanf("%d",&x)
      |               ^~~~~
answer.code:61:5: note: in expansion of macro ‘sc’
   61 |     sc(n);
      |     ^~