24556 John Biesnecker: Fun with John Horton Conway's Fractran. Internet 2013, 9p. 24576 Jörg Endrullis/Clemens Grabmayer/Dimitri Hendriks: Complexity of Fractran and productivity. Internet 2009, 18p. 24578 Richard Guy: Conway's prime producing machine. Math. Mag. 56/1 (1983), 26-33. Very good exposition. 24557 Dimitri Hendriks: Fractran. Internet (talk) 2011, 50p. 24555 Wikipedia: Fractran. Internet 2014, 8p. 24554 ZZ: Fractran. Internet (Esolang) 2009, 2p.