5172337

This number is a prime.

A prime formed from the concatenation in order of the four prime factors of the prime-digit 72335 that is the largest integer having the property “it and its square, 5232352225, both use only prime digits. Found by Zak Seidov” as Rivera notes, (see PC 72335). Also, note that 72335 consists of all the prime digits and 5172337 contains all the prime digits. [Loungrides]