#include <bits/stdc++.h>

using i64 = long long;
using u64 = unsigned long long;

typedef std::pair<long long, long long> PII;
const int mod = 998244353;
const int N = 2e6 + 1000;
const int INF = 0x3f3f3f3f;
const long long LINF = 1e18;
const double eps = 1e-12;
const double pi = std::acos(-1);
std::mt19937_64 rnd(std::random_device{}());

void solve() {
    i64 n, k;
    std::cin >> n >> k;
    std::vector<i64> a(n + 1), pre(n + 1), suf(n + 2);
    i64 ans = 0, res = 0;

    for (int i = 1; i <= n; i ++) std::cin >> a[i], ans = std::__gcd(ans, a[i]), res = std::__gcd(res, a[i] + k);
    for (int i = 1; i <= n; i ++) pre[i] = std::__gcd(pre[i - 1], a[i]);
    for (int i = n; i >= 1; i --) suf[i] = std::__gcd(suf[i + 1], a[i]);

    ans = std::max(ans, res);

    std::vector<PII> b;
    for (int i = 1; i <= n; i ++) {
        if (b.empty()) b.emplace_back(pre[i], i);
        if (b.back().first == pre[i]) {
            b.pop_back();
            b.emplace_back(pre[i], i);
        } else
            b.emplace_back(pre[i], i);
    }

    for (auto [preg, st] : b) {
        i64 g = 0;
        for (int r = st + 1; r <= n; r ++) {
            ans = std::max(ans, std::__gcd(std::gcd(preg, g), std::__gcd(a[r] + k, suf[r + 1])));
            g = std::__gcd(g, a[r] - a[r + 1]);
        }
    }

    std::cout << ans << "\n";
}

signed main() {
    std::ios::sync_with_stdio(false), std::cin.tie(nullptr), std::cout.tie(nullptr);
    
    int tmp = 1;
    
    std::cin >> tmp;

    while (tmp--)
        solve();

    return 0;
}