from math import isqrt

def sieve_twin_primes(n):
    is_prime = [True] * (n + 1)
    is_prime[0] = is_prime[1] = False
    for i in range(2, isqrt(n) + 1):
        if is_prime[i]:
            for j in range(i * i, n + 1, i):
                is_prime[j] = False
    twin_primes = []
    for i in range(2, n - 1):
        if is_prime[i] and is_prime[i + 2]:
            twin_primes.append(i)
    
    return twin_primes

twin_primes = sieve_twin_primes(10**7)

def solve():
    n = int(input())
    
    ok, ng = -1, len(twin_primes)
    
    while ng - ok > 1:
        mid = (ok + ng) // 2
        p = twin_primes[mid]
        if p * (p + 2) <= n:
            ok = mid
        else:
            ng = mid
    
    if ok == -1:
        print(-1)
    else:
        print(twin_primes[ok] * (twin_primes[ok] + 2))

T = int(input())

for _ in range(T):
    solve()