#include <bits/stdc++.h>

using namespace std;

#define int __int128
#define deg( x ) cerr<<""#x"="<<x<<endl
#define endl '\n'

const int N=3e5+10;

istream &operator>>( istream &in , __int128 &n ){
    string s; in>>s;
    n=0;

    for(char i:s) n=n*10+i-'0';

    return in;
}

ostream &operator<<( ostream &out , __int128 n ){
    if( n==0 ){
        out<<0;
        return out;
    }

    string s;

    while( n ){
        s+='0'+n%10;
        n/=10;
    }
    reverse( s.begin( ) , s.end( ) );
    out<<s;
    return out;
}

int idn=0;
int fan[ N ];

int A[ N ];
int up[ N ];
int ne[ N ];

void solve(){
    int n,k;
    cin>>n>>k;

    A[ n+1 ]=0;
    for( int i=1; i<=n; i++ ){
        cin>>A[ i ];
    }

    for( int i=1; i<=n; i++ ){
        up[ i ]=gcd( up[ i-1 ] , A[ i ] );
    }

    for( int i=n; i>=1; i-- ){
        ne[ i ]=gcd( ne[ i+1 ] , A[ i ] );
    }

    int ans=0;

    int cnt=0;
    int cnt2=0;
    for( int i=1; i<=n; i++ ){
        cnt=gcd( cnt , A[ i ] );
        cnt2=gcd( cnt2 , A[ i ]+k );
    }
    ans=max( max( cnt , cnt2 ) , ans );

    cnt=0;
    for( int i=1; i<=n; i++ ){
        ans=max( ans , gcd( cnt , ne[ i ] ) );
        cnt=gcd( cnt , A[ i ]+k );
    }

    cnt=0;
    for( int i=n; i>=1; i-- ){
        ans=max( ans , gcd( up[ i ] , cnt ) );
        cnt=gcd( cnt , A[ i ]+k );
    }
/*
//    vector<int> V;
//    V.emplace_back( 0 );
//
//    int e=1;
//    while( e<=n ){
//        int te=A[ e ];
//        while( A[ e ]==te ){
//            e++;
//            if( e==n+1 ) break;
//        }
//        V.emplace_back( te );
//    }
//
//    n=V.size()-1;
//    for( int l=1; l<=min( n , 1ll+50 ); l++ ){
//        cnt=0;
//        for( int o=1; o<l; o++ ) cnt=gcd( cnt , V[ o ] );
//        for( int r=max( l+1 , n-50 ); r<=n; r++ ){
//            int te=cnt;
//            for( int o=l; o<=r; o++ ){
//                te=gcd( te , V[ o ]+k );
//            }
//            for( int o=r+1; o<=n; o++ ) te=gcd( te , V[ o ] );
//
//            ans=max( ans , te );
//        }
//    }
 */

    int te=gcd( A[ 1 ] , A[ n ] );

    vector<int> V;
    int oo=te;
    for( int i=1; i<=n; i++ ){
        oo=gcd( oo , A[ i ] );
        V.emplace_back( oo );
    }

    oo=te;
    for( int i=n; i>=1; i-- ){
        oo=gcd( oo , A[ i ] );
        V.emplace_back( oo );
    }

    sort( V.begin() , V.end() );
    V.erase( unique( V.begin() ,  V.end() ) ,  V.end() );

    idn=0;
    for( auto x:V ){
        fan[ ++idn ]=x;
    }

    for( int i=idn; i>=1; i-- ){
        int now=fan[ i ];

        bool ok=false;
        int l=1;
        for( ; l<=n; l++ ){
            if( A[ l ]%now != 0 ){
                if( ( A[ l ]+k )%now == 0 ) break;
                else{
                    ok=true;
                    break;
                }
            }
        }

        if( ok ) continue;

        int r=l+1;
        for( ; r<=n; r++ ){
            if( ( A[ r ]+k )%now!=0 ){
                if( A[ r ]%now==0 ) break;
                else{
                    ok=true;
                    break;
                }
            }
        }

        if( ok ) continue;

        for( int e=r; e<=n; e++ ){
            if( A[ e ]%now!=0 ){
                ok=true;
                break;
            }
        }

        if( ok ) continue;

        ans=max( ans , now );
    }

    cout<<ans<<endl;

}

signed main() {
    ios::sync_with_stdio( 0 );
    cin.tie( 0 ); cout.tie( 0 );

    int T=1;
    cin>>T;

    while( T-- ){
        solve();
    }

    return 0;
}

In file included from /usr/include/x86_64-linux-gnu/c++/13/bits/stdc++.h:58,
                 from answer.code:1:
/usr/include/c++/13/numeric: In instantiation of ‘constexpr std::common_type_t<_Tp1, _Tp2> std::gcd(_Mn, _Nn) [with _Mn = __int128; _Nn = __int128; common_type_t<_Tp1, _Tp2> = __int128]’:
answer.code:54:20:   required from here
/usr/include/c++/13/numeric:166:21: error: static assertion failed: std::gcd arguments must be integers
  166 |       static_assert(is_integral_v<_Mn> && is_integral_v<_Nn>,
      |                     ^~~~~~~~~~~~~~~~~~
/usr/include/c++/13/numeric:166:21: note: ‘std::is_integral_v<__int128>’ evaluates to false
In file included from /usr/include/c++/13/bits/stl_pair.h:60,
                 from /usr/include/c++/13/bits/stl_algobase.h:64,
                 from /usr/include/c++/13/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/13/bits/stdc++.h:51:
/usr/include/c++/13/type_traits: In instantiation of ‘struct std::make_unsigned<__int128>’:
/usr/include/c++/13/type_traits:1983:11:   required by substitution of ‘template<class _Tp> using std::make_unsigned_t = typename std::make_unsigned::type [with _Tp = __int128]’
/usr/include/c++/13/numeric:173:24:   required from ‘constexpr std::common_type_t<_Tp1, _Tp2> std::gcd(_Mn, _Nn) [with _Mn = __int128; _Nn = __int128; common_type_t<_Tp1, _Tp2> = __int128]’
answer.code:54:20:   required from here
/usr/include/c++/13/type_traits:1836:62: error: invalid use of incomplete type ‘class std::__make_unsigned_selector<__int128, false, false>’
 1836 |     { typedef typename __make_unsigned_selector<_Tp>::__type type; };
      |                                                              ^~~~
/usr/include/c++/13/type_traits:1744:11: note: declaration of ‘class std::__make_unsigned_selector<__int128, false, false>’
 1744 |     class __make_unsigned_selector;
      |           ^~~~~~~~~~~~~~~~~~~~~~~~