#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<ll, ll>;
ll n, m, k;
const int N = 4e5 + 5;
const int P = 1e9 + 7;

void solve() {
    cin >> n >> k;
    vector<ll> a(n + 2);
    vector<ll> pre(n + 2), suf(n + 2);
    map<ll, vector<int>> mp1;
    map<ll, vector<int>> mp2;
    ll ans = 1;
    for (int i = 1; i <= n; i++) {
        cin >> a[i];
        pre[i] = __gcd(a[i], pre[i - 1]);
        mp1[pre[i]].push_back(i);
    }
    mp1[a[1] + k].push_back(1);
    mp2[a[n] + k].push_back(n);
    for (int i = n; i >= 1; i--) {
        suf[i] = __gcd(a[i], suf[i + 1]);
        mp2[suf[i]].push_back(i);
    }
    for (auto [x, y] : mp2) {
        if (mp1[x].size() == 0) {
            mp1[x].push_back(0);
        }
    }
    for (auto [x, y] : mp1) {
        if (mp2[x].size() == 0) {
            mp2[x].push_back(n + 1);
        }
    }
    for (auto [x, y] : mp1) {
        auto l = y[y.size() - 1];
        if (mp2[x].size()) {
            auto r = mp2[x][mp2[x].size() - 1];
            //  cout << x << ' ' << l << ' ' << r << ' ';
            if (l >= r) {
                ans = max(ans, x);
            } else {
                for (int i = l + 1; i <= r - 1; i++) {
                    if ((a[i] + k) % x != 0) {
                        break;
                    }
                    if (i == r - 1) {
                        ans = max(ans, x);
                    }
                }
            }
        }
    }
    cout << ans << '\n';
}
int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    int _ = 1;
    cin >> _;
    while (_--) {
        solve();
    }
    return 0;
}