29

This number is a prime.

The largest prime in the first case of primes of form 6*n+5 where n is an integer, i.e., 5, 11, 17, 23, 29. Note also that 29 is the smallest prime p in the first case of primes such that 6*p+5 are also primes, i.e., for p: 29, 31, 37, 41, 43 we create the primes 179, 191, 227, 251, 263. We also notice that the reverse concatenation of these primes p, i.e., 4341373129 is also prime. [Loungrides]