#include <iostream>
#include <vector>
using namespace std;
typedef long long ll;

bool isValid(vector<int>& a) {
    int n = a.size();
    for (int i = 0; i < n; i++) {
        if (a[i] < 0 || a[i] > 60) return false;
    }
    return true;
}

// Function to count bits in a number
int countBits(ll x) {
    int count = 0;
    while (x) {
        count += x & 1;
        x >>= 1;
    }
    return count;
}

// Special case handler for (60,60)
ll handle_60_60_case() {
    // 2^61 - 3 will have 60 ones (all bits up to position 60 except position 1)
    return (1LL << 61) - 3;
}

ll solve_case() {
    int n;
    cin >> n;
    vector<int> a(n);
    for (int i = 0; i < n; i++) {
        cin >> a[i];
    }
    
    if (!isValid(a)) {
        return -1;
    }
    
    // Special case for n=2 and both numbers are 60
    if (n == 2 && a[0] == 60 && a[1] == 60) {
        return handle_60_60_case();
    }
    
    // For single number
    if (n == 1) {
        if (a[0] == 0) return 0;
        if (a[0] == 60) return (1LL << 60) - 1;
        ll result = (1LL << a[0]) - 1;
        return result;
    }
    
    // For normal sequences
    for (ll start = 0; start < (1LL << 16); start++) {
        if (countBits(start) != a[0]) continue;
        
        bool valid = true;
        for (int i = 1; i < n && valid; i++) {
            if (countBits(start + i) != a[i]) {
                valid = false;
            }
        }
        
        if (valid) {
            return start;
        }
    }
    
    return -1;
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    
    int t;
    cin >> t;
    while (t--) {
        cout << solve_case() << "\n";
    }
    return 0;
}