1811

This number is a prime.

The smallest invertible prime p such that replacing each digit d in decimal expansion of p with d^2 yields a new prime, a semiprime and a sphenic number when done recursively three times, i.e., 1811-> 16411 (prime); 16411->1361611 (semiprime); 1361611->193613611 (sphenic number). [Bajpai]