191

This number is a prime.

(191, 251) is the only pair of 3-digit primes that can be represented as the product of two consecutive primes minus their sum, and to the product of the same primes plus their sum, 13*17 - (13+17) = 191, 13*17 + (13+17) = 251. Note that the concatenations in both orders of the elements of this pair, i.e., 191251 and 251191 are both primes. [Loungrides]