21123...07311 (27-digits)

This number is a prime.

                                               2112333 3111396533 8635107311

The prime formed by taking together the home primes (the first prime obtained after iterating the process of decomposing a number completely into its prime factors and concatenating the full prime decomposition) of all the composite digits 4, 6, 8, 9 which are 211, 23, 3331113965338635107, 311 respectively. [Beedassy]