#include <bits/stdc++.h>
#define int long long
using namespace std;
const double eps = 1e-8;

void solve() {
    int n, k, res = 0;
    cin >> n >> k;
    vector<int> a(n + 1), nxt(n + 1);
    for (int i = 1; i <= n; ++i)  cin >> a[i];
    nxt[n] = a[n];
    for (int i = n - 1; i >= 1; --i)  nxt[i] = __gcd(nxt[i + 1], a[i]);
    for (int i = 1, cur = 0; i <= n; ++i) {
        if(cur == 0 || a[i] % cur != 0) {
            if(cur == 0)  res = max(res, __gcd(a[i] + k, nxt[i + 1]));
            else  res = max(res, __gcd(cur, __gcd(a[i] + k, nxt[i + 1])));
            int d = cur;
            if(cur == 0)  d = abs(a[i + 1] - a[i]);
            else  d = __gcd(d, abs(a[i + 1] - a[i]));
            for (int r = i + 1; r <= n; ++r) {
                res = max(res, __gcd(d, __gcd(a[r] + k, nxt[r + 1])));
                if(r + 1 <= n)  d = __gcd(d, abs(a[r + 1] - a[r]));
            }
        }
        if(cur == 0)  cur = a[i];
        else  cur = __gcd(cur, a[i]);
    }
    cout << res << '\n';
}

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(0);  cout.tie(0);
    int t = 1;  cin >> t;
    while(t--) {
        solve();
    }
    return 0;
}