223 is a prime number.
223 is a number that cannot be written as a sum of three squares.
223 is the smallest prime with three prime digits. The sum of the digits of first primes up to 223 is 449.
223 is the smallest prime whose reversal has more than two prime divisors: 322 = 2 x 7 x 23.
223 is the final chapter of Mark Haddon's novel The Curious Incident of the Dog in the Night-Time, which uses just prime numbers for its chapters.
Source: Number Gossip