1. J. H. Conway, Unpredictable Iterations, Proceedings of the Number Theory Conference (University of Colorado, Boulder, CO, 1972), pp.49052. Also available in The Ultimate Challenge: The 3x + 1 Problem, Edited by Jeffrey C. Lagarias, American Mathematical Society, Providence, RI, 2010.
2. T. Oliveira e Silva, Empirical VeriÆcation of the 3x + 1 and Related Conjectures, in The Ultimate Challenge: The 3x + 1 Problem, Edited by Jeffrey C. Lagarias, American Mathematical Society, Providence, RI, 2010, pp.1890207.