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Truncatable primes (Posted on 2018-07-15) Difficulty: 3 of 5
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.

No Solution Yet Submitted by Ady TZIDON    
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Some Thoughts re: computer solution Comment 2 of 2 |
(In reply to computer solution by Charlie)

You say: ..." if we consider each of 2, 3, 5 and 7 to be considered a truncatable prime, then these are four more, making 15. Each is a prime, but actually if you truncate any one of these, nothing is left."

I also believe so, but the formal definition contradicts ours.

  Posted by Ady TZIDON on 2018-07-26 02:39:41
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