101111

This number is a prime.

101111 is prime when read as a base-two number. This is the last of only four primes in the first 10,000 that are both a prime when read as a base-two and a base-ten number. [Connolly]

The smallest prime concatenated from the binary representations of a twin prime pair. 101 (base 2) = 5 (base 10) concatenated with 111 (base 2) = 7 (base 10), with (5,7) the second twin prime pair. [Post]

The only six-digit prime whose digits are neither prime nor composite. [Gudipati]

The only six-digit anti-Yarborough prime. [Loungrides]

The first of four primes in strict succession, i.e., 101111, 101113, 101117 and 101119. [Harrison]