2389

This number is a prime.

(2389, 8923) is the only pair of primes formed from the concatenation in order of a prime-digit prime with successive digits, (2, 3) and a composite-digit prime with again successive digits, (8, 9), that are also powers of the previous prime digits, i.e., 8=2^3, 9=3^2. [Loungrides]