#include <bits/stdc++.h>
using namespace std;
#define int long long
const int maxn = 4e5 + 9;
int st[22][maxn];
int a[maxn];
int log2s[maxn];
void solve()
{
    int n;
    cin >> n;
    int k;
    cin >> k;
    for (int i = 1; i <= n; i++)
    {
        cin >> a[i];
        st[0][i] = a[i] + k;
    }
    for (int i = 1; i <= 21; i++)
    {
        for (int j = 1; j + (1 << i) - 1 <= n; j++)
        {
            st[i][j] = gcd(st[i - 1][j], st[i - 1][j + (1 << (i - 1))]);
        }
    }
    for (int i = 2; i <= n; i++)
        log2s[i] = log2s[i / 2] + 1;
    auto query = [&](int l, int r) -> int
    {
        if (l > r)
            return 0;
        int lgs = log2s[r - l + 1];
        return gcd(st[lgs][l], st[lgs][r - (1 << lgs) + 1]);
    };
    vector<array<int, 2>> pres{{0, 0}}, sufs{{n + 1, 0}};
    int pre = 0, suf = 0;
    for (int i = 1; i <= n; i++)
    {
        pre = gcd(pre, a[i]);
        if (pre == pres.back()[1])
        {
            pres.pop_back();
        }
        pres.push_back({i, pre});
    }
    for (int i = n; i >= 1; i--)
    {
        suf = gcd(suf, a[i]);
        if (suf == sufs.back()[1])
        {
            sufs.pop_back();
        }
        sufs.push_back({i, suf});
    }
    sort(pres.begin(), pres.end());
    sort(sufs.begin(), sufs.end());
    int ans = 0;
    for (auto [poss, pregcd] : pres)
    {
        int posl = poss + 1;
        for (auto [pos, sufgcd] : sufs)
        {
            int posr = pos - 1;
            if (posl <= posr)
            {
                ans = max(ans, gcd(gcd(pregcd, sufgcd), query(posl, posr)));
            }
        }
    }
    cout << ans << endl;
}
signed main()
{
    // freopen("data.in", "r", stdin);
    // freopen("data.out", "w", stdout);
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int t;
    cin >> t;
    while (t--)
        solve();
}