123400000000000004321

This number is a prime.

                                                     1 2340000000 0000004321

The smallest palindromic prime of the form 1234*10^(k + 4) + 4321, where k is the number of zeros between 1234 and 4321. The sequence of k producing primes begin 13, 19, 21, 37, 103, 121, 151, ... . [Honaker]