from math import isqrt

lim = 10**7 + 10
prime_flag = [1]*lim
prime_flag[0] = 0
prime_flag[1] = 0
for p in range(2,lim):
    if prime_flag[p]:
        for q in range(2*p,lim,p):
            prime_flag[q] = 0

t = int(input())
for i in range(t):
    n = int(input())
    if n <= 14:
        print(-1)
        continue
        
    r = isqrt(n+1) - 1
    while True:
        if prime_flag[r] & prime_flag[r+2]:
            print(r*(r+2))
            break
        r -= 1