Right Trunctable Primes

These are strange primes in that, if you successively remove the right-most digit another prime results, BUT even stranger is that if you coninue to do this, every "new [smaller]" number will also be prime. Here's an example:




   3             BTW, there is not a "next longer" one in this sequence since there are no primes between 37967 and 37987.


There are 15 primes which are both left-truncatable and right-truncatable. They have been called two-sided primes. The complete list:

2, 3, 5, 7, 23, 37, 53, 73, 313, 317, 373, 797, 3137, 3797, 739397


freeed freeed 61-65, M 6 Responses Apr 18, 2010

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Are there palindrome primes?


The first few (base-10) palindromic primes are 2, 3, 5, 7, 11, 101, 131, 151, 181, 191, 313, 353, 373, 383, 727, 757, 787.
Note these are neither right nor left trunctable in general since, say 787, becomes 78 or 87 by dropping the left or right digit and neither result is prime. Of course there are exceptional cases like 191 which is all three since removing digits results in 19 and 91, both prime.


i love the way you can feel a prime number. I had a bunch of numbers i felt were just reeally solid and I just found out they were all primes.

I am ashamed to have to admit I have forgotten my Mathematics,what exactly ARE prime numbers,I guess I could look it up on google however since you have contributed with your story..............:-)

A number is called prime when no other number aside from itself divides it with no remainder. One is not considered a prime number, but 2,3,5,7,11, etc, are.

Brieks07: also unpredictable. These numbers are God's monkey wrench; I mean why CAN'T they be divided evenly? Why shouldn't ALL numbers have factors?

Interesting. =)