#include <bits/stdc++.h>
using namespace std;

#define int long long
using i64 = long long;

struct ST {
    std::vector<std::vector<int>> st;
    int M;

    ST (std::vector<int> a) {
        const int n = a.size() - 1;
        const int M = std::log(n) + 1;
        st.assign(M + 1, std::vector<int> (n + 1));
        for (int i = 1; i <= n; i++) {
            st[0][i] = a[i];
        }

        for (int j = 1; j <= M; j++) {
            for (int i = 1; i + (1 << j) - 1 <= n; i++) {
                st[j][i] = __gcd(st[j - 1][i], st[j - 1][i + (1 << (j - 1))]);
            }
        }
    }

    int query(int l, int r) {
        if (l > r) return 0;
        int j = __lg(r - l + 1);
        return __gcd(st[j][l], st[j][r - (1 << j) + 1]);
    }
};


void solve() {
    int n, k;
    std::cin >> n >> k;
    std::vector<int> a(n + 1), b(n + 1);
    for (int i = 1; i <= n; i++) {
        std::cin >> a[i];
        b[i] = a[i] + k;
    }

    ST A(a), B(b);

    std::vector<int> left{1}, right{n};
    for (int i = 1; i < n; i++) {
        if (A.query(1, i) != A.query(1, i + 1)) {
            left.push_back(i + 1);
        }
    }

    for (int i = n; i >= 2; i--) {
        if (A.query(i, n) != A.query(i - 1, n)) {
            right.push_back(i - 1);
        }
    }

    int ans = A.query(1, n);

    for (auto l : left) {
        for (auto r : right) {
            if (l <= r) {
                ans = std::max(__gcd(__gcd(A.query(1, l - 1), A.query(r + 1, n)), B.query(l, r)), ans);
            }
        }
    }
    std::cout << ans << "\n";
}

signed main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(0);

    int t = 1;
    std::cin >> t;
    while (t --) {
        solve();
    }
}