#include<bits/stdc++.h>
using namespace std;
#define fast ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define dbg(a,b,c,d) cerr<<a<<"  "<<b<<"  "<<c<<"  "<<d<<endl;
#define kill(a) {cout<<a<<endl;continue;}
#define KILL(a) {cout<<a<<endl;return 0;}
#define debug cerr<<"Error Found"<<endl;
#define mem(a,b) memset(a,b,sizeof(a))
#define lcm(a, b) (a/__gcd(a,b))*b
#define w(t) cin>>t;while(t--)
#define pi  2 * acos(0.0)
#define endl "\n"
int t, cs = 0;
const int mxn = 1e4 + 3, mod = 1e9 + 7;
int dv[mxn];
void pre()
{
    for(int i = 1; i * i < mxn; i++)for(int j = i; j < mxn; j += i)dv[j]++;
}
int32_t main()
{
    pre();

    w(t)
    {
        int n;
        cin >> n;
        vector<pair<int,int>>v;
        for(int i = 0, a; i < n; i++)
        {
            cin >> a;
            int cnt = 0;
            for(int j = 1; j * j <= a; j++)
            {
                if(a % j == 0)
                {
                    cnt++;
                    cnt += (j != a / j);
                }
            }
            v.push_back(make_pair(cnt, -a));
        }
        sort(v.begin(), v.end());
        int k;
        cin >> k;
        k--;
        cout << -v[k].second << endl;
    }

}