#include <iostream>
using namespace std;
int main() {
int t;
cin>>t;
while(t--){
int n;
cin>>n;
int a[n];
for(int i=0;i<n;i++)
cin>>a[i];
int max=0,x;
for(int i=0;i<n;i++){
for(int j=i;j<n;j++){
x=a[i]%a[j];
if(x>max)
max=x;
}
}
cout<<max<<endl;
}
return 0;
}
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