* [[http://www.thebadbyte.com/2016/08/collatz-factoring.html|Collatz Factoring]]
  * [[https://arxiv.org/abs/1002.3973|Collatz Problem of Positive Integers]]
  * [[https://boinc.thesonntags.com/collatz/highest_steps.php|Highest Steps]]
  * [[http://oeis.org/wiki/Index_to_OEIS:_Section_3#3x1|OEIS Index]]