_{This problem is a programming version of Problem 37 from projecteuler.net}

The number has an interesting property. Being prime itself, it is possible to continuously remove digits from left to right, and remain prime at each stage: , , , and . Similarly we can work from right to left: , , , and .

Find the sum of primes that are both truncatable from left to right and right to left below .

NOTE: , , , and are not considered to be truncatable primes.