palindromic prime A palindromic prime is simply a prime which is a palindrome. Obviously this depends on the base in which the number is written (for example, Mersenne primes are palindromic base 2). When no radix is indicated, we assume the radix is 10. In base ten a palindrome with an even number of digits is divisible by 11. So 11 is the only palindromic prime with an even number of digits.