#include <bits/stdc++.h>
// #define int long long
#define inf 0x3f3f3f3f
#define ll long long
#define pii pair<int, int>
#define tii tuple<int, int, int>
#define db double
#define all(a) a.begin(), a.end()
using namespace std;
const int maxn = 3e5 + 10;
const int mod = 998244353;
int lg[maxn], pre[maxn], suf[maxn], arr[maxn], n, k;
struct STtable {
    int st[maxn][20];
    void init() {
        for (int j = 1; j < 20; j++)
            for (int i = 1; i + (1 << j) - 1 < n; i++)
                st[i][j] = __gcd(st[i][j - 1], st[i + (1 << (j - 1))][j - 1]);
    }
    int query(int l, int r) {
        if (l > r) return 0;
        int k = lg[r - l + 1];
        return __gcd(st[l][k], st[r - (1 << k) + 1][k]);
    }
} ST;
void solve() {
    cin >> n >> k;
    for (int i = 1; i <= n; i++) cin >> arr[i];
    pre[0] = suf[n + 1] = 0;
    for (int i = 1; i <= n; i++) pre[i] = __gcd(arr[i], pre[i - 1]);
    for (int i = n; i; i--) suf[i] = __gcd(arr[i], suf[i + 1]);
    for (int i = 1; i < n; i++) ST.st[i][0] = abs(arr[i] - arr[i + 1]);
    ST.init();
    int ans = 1;
    for (int i = 1; i <= n; i++) {
        if (pre[i] != pre[i - 1]) {
            for (int j = i; j <= n; j++) {
                int gcd = __gcd(pre[i - 1], suf[j + 1]);
                gcd = __gcd(gcd, arr[j] + k);
                gcd = __gcd(gcd, ST.query(i, j - 1));
                ans = max(ans, gcd);
            }
        }
    }
    cout << ans << "\n";
}
signed main() {
    // freopen("1.in", "r", stdin);
    // freopen("1.out", "w", stdout);
    ios::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);
    for (int i = 2; i < maxn; i++) lg[i] = lg[i >> 1] + 1;
    int t = 1;
    cin >> t;
    while (t--) solve();
    return 0;
}