Finds bidirectionally-truncatable primes

gistfile1.py

def mark(sieve, x):
    for i in xrange(2*x, len(sieve), x):
        sieve[i] = False

sieve = [True] * 1000001
sieve[0], sieve[1] = False, False
for x in xrange(2, int(len(sieve) ** 0.5) + 1):
    if sieve[x]:
        mark(sieve, x)

def check_rtl(n):
    while n > 0:
        if sieve[n]:
            n = n/10
        else:
            return False
    return True

def check_ltr(n):
    place = len(str(n)) - 1
    while n > 0:
        if sieve[n]:
            n = n % 10**place
            place -= 1
        else:
            return False
    return True

counter = 0
i = 11 # smallest two-digit prime
while counter < 11: # total number of bi-truncatable primes
    if check_rtl(i) and check_ltr(i):
        print(i)
        counter += 1
    i += 1