#include <cstdio>
#include <cstdlib>
#include <cassert>
#include <algorithm>
#include <vector>
#include <iostream>
#include <tuple>
#include <iomanip>
#include <string>
#include <ctime>

using namespace std;

using ll = long long;

const int MAX_N = 50000;
const int MAX_A = 50000;

inline int gcd(int a, int b) {
  return b ? gcd(b, a%b) : a;
}

void solve() {
  int N; cin >> N;
  assert(2 <= N && N <= MAX_N);

  int g = 0;
  for(int i = 1; i <= N; i++) {
    int a; assert(cin >> a); assert(1 <= a && a <= MAX_A);
    g = gcd(g, a);
  }

  cout << (g == 1 ? 0 : -1) << endl;
}

int main() {
#ifdef IN_MY_COMPUTER
  freopen("rd19.in", "r", stdin);
#else
  cin.tie(nullptr);
  ios_base::sync_with_stdio(false);
#endif

  int T; assert(cin >> T);
  assert(1 <= T && T <= 100);
  while(T--) {
    solve();
  }
  return 0;
}