#include<bits/stdc++.h>
using namespace std;
int main(){
    int t; 
    cin>>t;
    while(t--){
        int n,a[100],res=0;
        cin>>n;
        for(int i=0;i<n;i++) 
        	cin >> a[i];
        for(int i=0;i<n;i++){
            for (int j=i+1;j<n;j++){
                int x=a[i],y=a[j],d=abs(x-y);
                if(x==y) res=max(res,x+1);
                for(int k=1;k<=d;k++){
                    if(d%k==0){
                        int g1=x+(k-x%k)%k;
                        int g2=y+(k-y%k)%k;
                        while(g2){
                            int tmp=g2;
                            g2=g1%g2;
                            g1=tmp;}
                        res=max(res,g1);}
                }
            }
        }
        cout<<res<<endl;
    }
    return 0;
}
 

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