Some later nodes that refer to this trick are Re: Simple primality testing, Re^2: The Oldest Plays the Piano, Re: Calculate prime factors for a given number in a perl one-liner, Re: is it prime?.

Update 2015-10-22: See also "How does this regular expression work?" (2010-07) question on StackOverflow which asks about a similar regex in the article "A regular expression to check for prime numbers" (2007-03) by Avinash Meetoo