2689
This number is a prime.
Concatenate (right-to-left) the 2nd, 6th, 8th, and 9th prime and you will get another prime, i.e., 2319133. [Bopardikar]
The smallest of four primes concatenated from the digits that are the complementary of the single-digit powers of 2. The other are: 6829, 8269, 8629. [Loungrides]
(There is one curio for this number that has not yet been approved by an editor.)
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