2999
This number is a prime.
The fourth term of the sequence 2, 11, 29, 2999, ... , where each term (starting with the first prime) is the smallest prime, greater than the previous term, which contains a sum of digits equal to the previous term. The fifth term (5 * 10^333 - 10^332 - 10^174 - 1) was found by Jim Fougeron of Omaha, Nebraska.
Start with any number greater than 1, and write down all
its divisors, including 1 and itself. Now take the sum of
the individual digits of these divisors. After repeating
the process, you'll eventually get the product of the first
two odd primes (fifteen) or what Dr. Michael W. Ecker
describes as a "mathemagical black hole" with respect to
this particular iteration. Note that Jason Earls of
Blackwell, Oklahoma, found that 2999 is the least prime
that takes exactly fifteen steps to reach the fifteen
black hole.
2999 = 3 * 103 - 1 is prime, and so are
3 * 103 + 1 and 10 * 310 - 1. [Hartley]
The smaller term in the largest twin prime pair that sandwiches a palindromic number in Roman numerals (MMM). [Beedassy]
The year New York pizza delivery boy Philip J. Fry wakes up
in the pilot episode of Futurama. [Cohen]
2999 is the fourth and largest known primorial (2999#) such that 2999#+1 is divided by the next prime after 2999, i.e., 3001. [Rivera]