palindromic prime

A prime number $p$ that in a given base $b$ is also a palindromic number. Although there are infinitely many palindromic numbers in any given base, it is not known if the same is true of palindromic primes.

If $b+1$ is prime, then it is the only palindromic prime in base $b$ to have an even number of digits; all other palindromes with an even number of digits will be multiples of $b+1$.