1123

This number is a prime.

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The smallest prime, concatenated from two double-digit primes p, q such that their concatenation in the other order, i.e., 2311, is also prime. [Loungrides]

The only prime less than a googol formed from the smallest double-digit prime, (11), following the procedure “each next digit or 2-digit number can be represented as the sum of its two previous digits.” [Loungrides]