#include <bits/stdc++.h>
using namespace std;

#define PB push_back
#define F first
#define S second
#define MP make_pair
#define LL long long
#define ULL unsigned long long
#define LB lower_bound
#define MOD1 1000000007
#define MOD2 1000000009
#define INF LONG_MAX
#define pr(i,x,n) for(int ii=i;ii<n+i;ii++){cout<<x[ii]<<" ";}cout<<endl;
#define ip(i,x,n) for(int ii=i;ii<n+i;ii++){cin>>x[ii];};
#define db(x,y) cout<<x<<" "<<y<<endl;
#define N 400100
#define LD long double
#define PR pair<LD,LL>

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    LL n,i,j,l,t,m,x,k,y,q,z,a[N],b[N],mx,ans[N],x1,y1;
    string s,p;
    cin>>t;
    while(t--)
    {
    	k=0;
    	cin>>n;
    	cin>>k;
    	for(i=1;i<n;i++)
    	{
    		cin>>x;
    		k=__gcd(k,x);
    	}
    	if(k==1)
    	cout<<0<<endl;
    	else
    	cout<<-1<<endl;
    }
}