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Truncatable primes: Difference between revisions
Number base is 10
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A truncatable prime is a prime number that when you successively remove digits from one end of the prime, you are left with a new prime number; for example, the number 997 is called a ''left-truncatable prime'' as the numbers 997, 97, and 7 are all prime. The number 7393 is a ''right-truncatable prime'' as the numbers 7393, 739, 73, and 7 formed by removing digits from its right are also prime. No zeroes are allowed in truncatable primes.
The task is to find the largest left-truncatable and right-truncatable primes less than one million (base 10 is implied).
C.f: [[Sieve of Eratosthenes]]; [http://mathworld.wolfram.com/TruncatablePrime.html Truncatable Prime] from Mathworld.
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