This number is a prime.
All the residences in Primes Lane in Holton, Suffolk, England, have a prime postcode. Primes Lane leads southwards into the B1123 main road. [Croll]
11/23 (November 23) is the only date containing the concatenation of two 2-digit primes that can be read as a prime number in either "month-day" or "day-month" format, i.e., 11/23 or 23/11. Note that Kinro Kansha no Hi (Labor-Thanksgiving Day) occurs on this date in Japan. [Kik]
The smallest zeroless prime showing three consecutive digits. [Silva]
The sums of the first digits, middle digits, last digits and all digits are the four single-digit primes. [Silva]
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]
"1123 Hard to Believe Facts" is a wonderful book packed from beginning to end with factual information on a variety of subjects. [Kostov]