def check(a, b):
# print a, b
if (a,b) in cache:
return cache[(a,b)]
else:
p1 = int(str(a)+str(b))
p2 = int(str(b)+str(a))
retval =(p1 in primes_s and p2 in primes_s) or (c_prime.is_prime(p1) and c_prime.is_prime(p2))
cache[(a,b)] = retval
return retval
def solve(length):
odd = set(("1","3","5","7","9"))
retval = None
for digits in permutations(map(str, range(1,length+1)), length):
if digits[-1] in odd:
num = int("".join(digits))
if c_prime.is_prime(num):
retval = num
return retval
