What is a Truncatable Prime number?

In number theory, a left-truncatable prime is a prime number which, in a given base, contains no 0, and if the leading ("left") digit is successively removed, then all resulting numbers are prime. For example, 9137, since 9137, 137, 37 and 7 are all prime. Decimal representation is often assumed and always used in this article.

A right-truncatable prime is a prime which remains prime when the last ("right") digit is successively removed.

The largest is the 24-digit 357686312646216567629137.

Step 1: 357686312646216567629137. Prime!

Step 2: 57686312646216567629137. Prime!

Step 3: 7686312646216567629137. Prime!

Step 4: 686312646216567629137. Prime!

Step 5: 86312646216567629137. Prime!

Step 6: 6312646216567629137. Prime!

Step 7: 312646216567629137. Prime!

Step 8: 12646216567629137. Prime!

Step 9: 2646216567629137. Prime!

Step 10: 646216567629137. Prime!

Step 11: 46216567629137. Prime!

Step 12: 6216567629137. Prime!

Step 13: 216567629137. Prime!

Step 14: 16567629137. Prime!

Step 15: 6567629137. Prime!

Step 16: 567629137. Prime!

Step 17: 67629137. Prime!

Step 18: 7629137. Prime!

Step 19: 629137. Prime!

Step 20: 29137. Prime!

Step 21: 9137. Prime!

Step 22: 137. Prime!

Step 23: 37. Prime!

Step 24: 7. Prime!

Truncatable prime numbers are indeed interesting!

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Credits: WP