353373383727383373353

This number is a prime.

                                                     3 5337338372 7383373353

The only palindromic prime formed by concatenating four consecutive 3-digit palindromic primes in the pattern {a, b, c, d, c, b, a}, i.e., {353, 373, 383, 727, 383, 373, 353}. [Bajpai]