19991

This number is a prime.

The smallest invertible primemirp. [Bhattacharya]

The larger of the only two five-digit palindromic primes formed from two primes (19 and 991), one of which is the sum of the digits of the other. [Silva]

The smallest palindromic prime that is the sum of 17 consecutive prime numbers (1109 + ... + 1231 = 19991). [Schuler]

The smallest palindromic Sophie Germain prime p such that p! and p^p both contain p as a string of the digits. Note that 19991 is an invertible prime also. [Bajpai]