739397 is a prime number. If you get rid of any number of digits from either the right side or the left side (but not both) the number you are left with is a prime (as long as you don't remove all the digits and are left with nothing. This is the largest number that has this property.
This is called a "two sided prime". A "left truncatable prime" is a prime where you can cut off any number of digits from the left and still get a prime. A "right truncatable prime" is a prime where you can get rid of any number of digits from the right and still have a prime. A "two sided prime" is both.
The 15 numbers that are considered two sided primes include 1 digit prime numbers that don't have anything you can take away.
2, 3, 5, 7, 23, 37, 53, 73, 313, 317, 373, 797, 3137, 3797, 739397
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