import sys
primes = range(5,1001)
found_primes = [2,3]
for i in primes:
for j in found_primes:
is_prime = True
if i % j == 0:
is_prime = False
break
if j*j > i:
break
if is_prime:
found_primes.append(i)
def is_prime(k):
return k in found_primes
def is_palindrome(k):
a = str(k)
return a == a[::-1]
t = int(sys.stdin.readline())
for i in range(t):
n = int(sys.stdin.readline())
vals = sys.stdin.readline().split()
vals = map(int, vals)
for val in vals:
if is_prime(val) and is_palindrome(val):
print val
break
