654781329

This number is a composite.

654781329 = 3^2 x 72753481 is the only integer with just two distinct prime factors, which is also "penholodigital" (using each nonzero digit once and only once) and whose reversal is a square: 923187456 = 2^8 x 3^4 x 211^2 = 30384^2. [Post]