19249

This number is a prime.

Real primes congruent to 2 modulo 3 are also Eisenstein primes. In May 2007, the 3.9 million-digit prime 19249*2^13018586+1 became the largest known real Eisenstein prime. It was found as part of the Seventeen or Bust project and at the time of its discovery was the largest known Colbert number. [Caldwell]