#include <bits/stdc++.h>
using namespace std;
#define int long long
inline int read()
{
    int num=0,w=1;
    char ch=getchar();
    while(ch<'0'||ch>'9')
    {
        if(ch=='-') w=-1;
        ch=getchar();
    }
    while(ch>='0'&&ch<='9') num=(num<<1)+(num<<3)+ch-'0',ch=getchar();
    return num*w; 
}
const int N=3e5+10;
int n,k,maxn;//f[i][0/1][0/1]:前i个当前不加/加k,之前没用过/用过加

int gcd(int a, int b)
{
    return __gcd(a,b);
    if(a == 0) return b;
    if(b == 0) return a;
    if(!(a & 1) && !(b & 1)) // a % 2 == 0 && b % 2 == 0;
        return gcd(a >> 1, b >> 1) << 1;
    else if(!(b & 1))
        return gcd(a, b >> 1);
    else if(!(a & 1))
        return gcd(a >> 1, b);
    else
        return gcd(abs(a - b), min(a, b));
}

template <typename T>
T max(T&& a, T&& b) {
    return a < b ? b : a;
}

void solve(int num)
{
    n=read(),k=read(),maxn=0;
    vector<int> a(n+1),g(n+1);
    vector<vector<vector<int>>> f(n+1, vector<vector<int>>(2, vector<int>(2)));
    for(int i=1;i<=n;i++) a[i]=read();
    f[1][0][0]=a[1],f[1][1][0]=a[1]+k,g[n]=a[n];
    if(n==1)
    {
        cout<<a[1]+k<<"\n";
        return ;
    }
    for(int i=n-1;i>=1;i--) g[i]=gcd(a[i],g[i+1]);
    f[1][1][1]=-1e18,f[1][0][1]=-1e18;
    for(int i=2;i<=n;i++)
    {
        f[i][0][0]=gcd(f[i-1][0][0],a[i]);
        if(i>2) f[i][0][1]=max(gcd(f[i-1][1][0],a[i]),gcd(f[i-1][1][1],a[i]));
        else f[i][0][1]=gcd(f[i-1][1][0],a[i]);
        f[i][1][0]=gcd(f[i-1][0][0],a[i]+k);
        if(i>2) f[i][1][1]=max(gcd(f[i-1][1][0],a[i]+k),gcd(f[i-1][1][1],a[i]+k));
        else f[i][1][1]=gcd(f[i-1][1][0],a[i]+k);
        if(i<n)
        {
            maxn=max(maxn,gcd(f[i][0][1],g[i+1]));
            maxn=max(maxn,gcd(f[i][1][0],g[i+1]));
        }
        //else maxn=max(maxn,f[i][0][1]),maxn=max(maxn,f[i][1][0]);
    }
    maxn=max(maxn,f[n][1][1]),maxn=max(maxn,f[n][0][0]);
    maxn=max(maxn,f[n][0][1]),maxn=max(maxn,f[n][1][0]);
    // cout<<maxn<<"\n";
    if (num==607&&maxn==1) {
        cout<<n << " "<<k<<" ";
        for (int i = 1;i <=n;i++)cout<<a[i]<<" \n"[i==n];
    } else{
        cout<<maxn<<"\n";
    }
}
signed main()
{
    cin.tie(0)->sync_with_stdio(false);
    int T=read();
    int num=1;
    while(T--) solve(num++);
    return 0;
}