#include <bits/stdc++.h>
#define dd(x) cout << #x << "\n"
#define d(x) cout << #x  << ": " << x << "\n"
#define SZ(x) ((int)(x).size())
using namespace std;
#define int long long
using pii = pair<int, int>;
using vpii = vector<pii>;
using vi = vector<int>;
using vii = vector<vector<int>>;
using a3 = array<int, 3>;
using ll = long long;
const int inf = 0x3f3f3f3f3f3f3f3fLL;

#define MULTI_TEST

void solve() {
    int n, k; cin >> n >> k;
    vector<int> a(n + 1), pr(n + 1), ed(n + 2), nxt(n + 2);
    vector f(n + 1, vector<int> (20)); 
    vector<int> logx(n + 1);
    for(int i = 2; i <= n; i++) logx[i] = logx[i / 2] + 1;

    for(int i = 1; i <= n; i++) {
        cin >> a[i]; 
        f[i][0] = abs(a[i] - a[i - 1]);
        pr[i] = gcd(pr[i - 1], a[i]);
    }
	
	for(int j = 1; j < 20; j++) {
		for(int i = 1; i + (1 << (j - 1)) <= n; i++) {
			f[i][j] = gcd(f[i][j - 1], f[i + (1 << (j - 1))][j - 1]);
		}
	}

    auto rg = [&](int l, int r) {
        if(l > r) return 0LL;
        int len = r - l + 1;
        return gcd(f[l][logx[len]], f[r - (1 << logx[len]) + 1][logx[len]]);
    };

    for(int i = n; i; i--) {
        ed[i] = gcd(ed[i + 1], a[i]);
        
        if(ed[i] != ed[i + 1]) {
            nxt[i] = i + 1;
        } else {
            nxt[i] = nxt[i + 1];
        }
    }

    int ans = rg(1, n);
    for(int l = 1; l <= n; l++) {
        ans = max(ans, gcd(
            gcd(pr[l - 1], a[l] + k),
            ed[l + 1]
        ));

        int gcdv = gcd(pr[l - 1], a[l] + k);
        int r = l + 1;
        while(r <= n) {
            ans = max(ans, gcd(
                gcdv, gcd(
                    rg(l + 1, r), ed[r + 1]
                )
            ));
            if(r == n) break;
            r = nxt[r + 1] - 1;
        }
    }

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

signed main() {
    ios::sync_with_stdio(false); cin.tie(0);
#ifdef MULTI_TEST
    int T; cin >> T;
#else
    int T = 1;
#endif
    while(T--) solve();
    return 0;
}

/*

1
7 8
1 6 6 6 12 12 48

2
6 2
5 3 13 8 10 555
3 0
3 6 9

*/