The number 3797 has an interesting property. Being prime itself, it is possible to continuously remove digits from left to right, and remain prime at each stage: 3797, 797, 97, and 7. Similarly we can work from right to left: 3797, 379, 37, and 3.
Find the sum of the only eleven primes that are both truncatable from left to right and right to left.
NOTE: 2, 3, 5, and 7 are not considered to be truncatable primes.
I can't figure out the eleven prime numbers, why are these prime numbers wrong: 11 13 17 23 31 37 53 71 73 113 131
aren't they all truncatable from both left and right? and if they are, there are still many more truncatable prime numbers from both left and right... what am I doing wrong?