#include<bits/stdc++.h>
using namespace std;
const int N = 3e5+10;
int a[N];
int glast[N];
int gcd(int x,int y){
    if(!y) return x;
    return gcd(y,x%y);
}
void solve(){
    int n,k;
    cin>>n>>k;
    for(int i=1;i<=n;i++) cin>>a[i];
    glast[n+1]=0;
    for(int i=n;i>=1;i--){
        glast[i]=gcd(glast[i+1],a[i]);
    }
    int g=0;
    int ans=0;
    for(int i=1;i<=n;i++){
        int x=gcd(g,a[i]);
        if(x!=g){
            int tmp=0;
            for(int j=i+1;j<=n;j++){
                int now = gcd(x,tmp);
                now = gcd(now,glast[j+1]);
                now = gcd(now,a[j]+k);
                
                ans=max(ans,now);
                tmp = gcd(tmp,abs(a[j]-a[j+1]));
            }
        }
        g=x;
    }
    cout<<ans<<endl;
}
int main(){
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int T=1;
    cin>>T;
    while(T--) solve();
    return 0;
}