#include <bits/stdc++.h>

#define FILE "good"
#define USE_FREOPEN 0
#define USE_LONG 0
#define USE_IOSOPT 1

#if USE_LONG
typedef long long ll;
typedef unsigned long long ull;
#else
typedef int ll;
typedef unsigned int ull;
#endif
typedef unsigned int ill;
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define rm erase
#define ins insert
#define elsif else if
#define skip(a) if((a)) continue;
#define skipn(a) unless((a)) continue;
#define unless(a) if(!(a))
#define p(a, b) pair < a, b >
#define sq(x) ((x) * (x))
#define rev(a) reverse(a.begin(), a.end())
#define ord(a) sort(a.begin(), a.end())
#define rs resize
#define sz size
#define readv(a, n, tp) \
    for(int i = 0; i < n; i++) \
    { \
        tp d; \
        cin >> d; \
        a.pb(d); \
    }
#define printv(a) \
    for(auto lsti = a.begin(); lsti != a.end(); lsti++) \
    { \
        cout << *lsti << ' '; \
    }
#define die(a) \
    { \
        cout << a << endl; \
        exit(0); \
    }

using namespace std;

const ill MAXN = (ll)5e4;

struct node {
    ll gcdx;
    node() {
        gcdx = 0;
    }
} t[MAXN * 4];
ll data[MAXN];

void build(ill node, ill l, ill r)
{
    if(l == r)
    {
        t[node].gcdx = data[l];
        return;
    }
    ill mid = (l + r) / 2;
    build(node * 2, l, mid);
    build(node * 2 + 1, mid + 1, r);
    t[node].gcdx = __gcd(
            t[node * 2].gcdx,
            t[node * 2 + 1].gcdx);
}

void print(ill node, ill l, ill r, ill lvl = 0)
{
    for(int i = 0; i < lvl; i++)
        cout << "  ";
    cout << node << "(" << l << ", " << r << ").gcdx = " << t[node].gcdx;
    if(l == r)
    {
        cout << "; data[" << l << "] = " << data[l];
        cout << endl;
        return;
    }
    cout << endl;
    ill mid = (l + r) / 2;
    print(node * 2, l, mid, lvl + 1);
    print(node * 2 + 1, mid + 1, r, lvl + 1);
}

ll get(ill node, ill l, ill r, ill tl, ill tr)
{
//  cout << node << "(" << tl << ", " << tr << ").gcdx = " << t[node].gcdx << endl;
    if(tl > r || tr < l)
        return 0;
    if(tl >= l && tr <= r)
        return t[node].gcdx;
    ill mid = (tl + tr) / 2;
    return __gcd(
            get(node * 2, l, r, tl, mid),
            get(node * 2 + 1, l, r, mid + 1, tr));
}

ll get(ill l, ill r, ill n)
{
    return get(1, l, r, 0, n - 1);
}

ll sqrtt(ll n)
{
    ll sqn = sqrt(n);
    return (sq(sqn) == n ? sqn : -1);
}

int main()
{
#if USE_IOSOPT
    ios_base::sync_with_stdio(false);
            cin.tie(0);
#endif
#if USE_FREOPEN
    freopen(FILE".in", "r", stdin);
    freopen(FILE".out", "w", stdout);
#endif
    ll tc;
    cin >> tc;
    while(tc--)
    {
        ll n;
        cin >> n;
        memset(data, 0, sizeof(data));
        for(int i = 0; i < n; i++)
        {
            cin >> data[i];
        }
        ll tn = n;
        n = 1;
        while(n < tn)
            n <<= 1;
        build(1, 0, n - 1);
//      print(1, 0, n - 1);
        ll l = 0, r = tn, ans = 0;
        while(l <= r)
        {
            ll m = (l + r) / 2;
//          cout << l << ' ' << r << ' ' << m << endl;
            ll tru = 0;
            for(int i = 0; i < (tn - m + 1); i++)
            {
                ll val = get(i, i + m - 1, n);
//              cout << "\t" << i << ' ' << (i + m - 1) << ' ' << val << endl;
                tru |= (val != 1);
            }
            if(tru)
                l = m + 1;
            else
            {
                r = m - 1;
                ans = m;
            }
        }
        cout << (ans > 1 ? ans : -1) << endl;
    }
}