//on the name of Allah:)
#include<bits/stdc++.h>
#define int         long long
#define endl        "\n"
#define pi          2 * acos(0.0)
#define mod         1000000007
#define Mul(a,b)    (a%mod * b%mod)%mod
#define Add(a,b)    (a%mod + b%mod)%mod
#define all(x)      (x).begin(),(x).end()
#define allr(x)     (x).rbegin(),(x).rend()
#define gcd(x, y)   (__gcd(x, y))
#define lcm(x, y)   ((x/gcd(x, y))*y)
#define faster      cin.tie(NULL), cout.tie(NULL);
#define TC          int t ; cin>>t ; while (t--)
const int N = 1e9 + 7;
using namespace std;

int divisors (int n)
{
    vector<int>divs;
    for(int i = 1 ; i*i <= n ; i++) {
        if(n % i == 0) {
            divs.push_back(i);
            if(n/i != i) {
                divs.push_back(n/i);
            }
        }
    }
    sort(divs.begin(),divs.end());


    return divs.size();
}

bool cmp (pair<int,int>a,pair<int,int>b) {
    if(a.second == b.second) {
        return a.first>b.first;
    }
    return a.second<b.second;
}

void s()
{
    int n,k;
    cin >> n;
    vector<int>v;
    for(int i=0;i<n;i++) {
        int x;
        cin >> x;
        v.push_back(x);
    }
    cin >> k;
    vector<pair<int,int>>d;
    for(int i=0;i<n;i++) {
        int cnt = divisors(v[i]);
        d.push_back({v[i],cnt});
    }

    sort(all(d),cmp);

    cout << d[k-1].first << endl;
}
int32_t main()
{   ios::sync_with_stdio(false);

    TC
    s();


}