Jim Carrey claims to have been obsessed with The Number 23 long before being a part of the movie. His production company is called JC 23 Entertainment. It was coincidence that his father was an accountant and he played the saxophone, like his character in the movie.
The plot is largely based on the philosophical writings of William S. Burroughs, who came to believe that the number 23 held mystical significance after encountering it during significant moments in his life. Burroughs eventually wrote the screenplay "The Last Words of Dutch Schultz" around this concept, in which he used the deathbed ramblings of mobster Dutch Schultz as a springboard for telling a story based around Schultz's life - which, in Burrough's vision, revolved around recurrences of the number 23.
The DVD contains exactly 23 chapters.
(at around 48 mins) The telephone number for the King Edward Hotel (which is printed on the room keys) is 555-1232. Not only is there a 23 and a 32 (a reverse 23) in the second half of the number, but 5+5+5+1+2+3+2 is equal to 23.