Take the prime number 3797. It has an interesting property. Remove continuously digits from the left, one by one, and it remains prime at each stage: 3797, 797, 97, and 7.

Similarly, we can work from right to left: 3797, 379, 37, and 3.

List the only eleven primes that are truncatable both from left to right and from right to left.

Rem: Each of 2, 3, 5, and 7 is considered a truncatable prime.