A prime number generator

http://bit-player.org/2015/pumping-the-primes

This curious generator of primes was discovered in 2003, during a summer school exploring Stephen Wolfram’s “New Kind of Science.” ...During the summer school, Frank and his group ...observed no composite numbers, but their conjecture that the value is always 1 or prime remained unproved. One of the students present that summer was Eric S. Rowland, who had just finished his undergraduate studies and was about undertake graduate work with Doron Zeilberger at Rutgers. In 2008 Rowland took another look at the gcd-based prime generator and proved the conjecture.