def sieve_of_eratosthenes(n):
    # 1からnまでのリストを作成
    primes = [True] * (n + 1)
    p = 2
    while (p * p <= n):
        if primes[p]:
            # pの倍数を除去
            for i in range(p * p, n + 1, p):
                primes[i] = False
        p += 1
    # 残った数をリストに追加
    return [p for p in range(2, n + 1) if primes[p]]
p = sieve_of_eratosthenes(10**7+10)
p_set = set(p)
a = []
for i in p:
    if(i+2 in p_set):a.append(i)

T = int(input())
for _ in range(T):
    N = int(input())
    if(N < 15):
        print(-1)
        continue

    ok,ng = 0,len(a)
    while(ng - ok > 1):
        mid = (ok+ng)//2
        if(a[mid]*(a[mid]+2) <= N):
            ok = mid
        else:
            ng = mid
    print(a[ok]*(a[ok]+2))