Problems & Puzzles: Puzzles

Puzzle 796. Looking for certain palprimes

As you know, "palindromic number or numeral palindrome is a number that remains the same when its digits are reversed".

I propose you to construct a special kind of numeral palindrome, and test for the primality of it.

Construct the palindrome the following way:

a) concatenate the natural numbers from 1 to n, obtaining A
b) reverse A obtaining B
c) concatenate A and B omitting the first digit of B, obtaining the palindrome P(n)

Q. What is the smallest such prime P(n)?

Contribution came from Jan van Delden


Jan wrote:

There are no prime solutions (n<=6794, digits(P(n))<=52137).
The answer to your question is therefore: I donít know.
But if we change the last step c) to:
c) concatenate B and A omitting the first digit of A, obtaining the palindrome Q(n)
There are 3 prime solutions (n<=6801, digits(Q(n))<=52193).
Q(31) 105 digits, Q(59) 217 digits and Q(113) 461 digits are certified prime.
The smallest solution is:


Records   |  Conjectures  |  Problems  |  Puzzles