Project Euler 第37题

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.

3797是一个奇特的素数，依次从左到右去掉一个数字，得到的数字仍然为素数，同样从右到左，也会素数。一共有11个这样的素数，求他们的和。