#include<bits/stdc++.h>
using namespace std;
#define MAXN 1e6+5
int spf[1000008],a[500005],b[1000005];
vector<int>prime;
vector<int>cal[1000001];
void sieve()
{
    spf[1] = 1;
    for (int i=2; i<MAXN; i++)
        spf[i] = i;
    for (int i=4; i<MAXN; i+=2)
        spf[i] = 2;
    for (int i=3; i*i<MAXN; i++)
    {
        if (spf[i] == i)
        {
            for (int j=i*i; j<MAXN; j+=i)
                if (spf[j]==j)
                    spf[j] = i;
        }
    }
    prime.push_back(2);
    for(int i=3;i<MAXN;i+=2)
    {
        if(spf[i]==i)
            prime.push_back(i);
    }
}
vector<int> getFactorization(int x)
{
    vector<int> ret;
    while (x != 1)
    {
        if(ret.empty()||(ret.back()!=spf[x]))
            ret.push_back(spf[x]);
        x = x / spf[x];
    }
    return ret;
}
int main()
{
     int t,n,m,x,y,z,i,j,k;
     sieve();
     for(i=1;i<=1000000;i++)
        cal[i]=getFactorization(i);
     scanf("%d",&t);
     while(t--)
     {
         scanf("%d",&n);
         for(i=1;i<=n;i++)scanf("%d",&a[i]);
         set<int>s;
         vector<int>p;
         x=0;
         i=1;
         j=1;
         z=i;
         while(j<=n&&i<=n)
         {
             y=0;
             for(k=0;k<cal[a[j]].size();k++)
             {
                 if(b[cal[a[j]][k]])
                 {
                     y=1;break;
                 }
             }
             if(y)
             {
                 x=max(x,j-i);
                 i++;
                 for(k=0;k<cal[a[z]].size();k++)
                    b[cal[a[z]][k]]=0;
                 z=i;
             }
             else
             {
                  for(k=0;k<cal[a[j]].size();k++)
                    b[cal[a[j]][k]]=1;
                 j++;
             }
         }
         x=max(x,j-i);
         if(x==1)
            printf("-1\n");
         else
            printf("%d\n",x);
         for(i=0;prime[i]<=1000000&&i<prime.size();i++)b[prime[i]]=0;
     }
}