Iteration of the number-theoretic function f(2n) = n, f(2n + 1) = 3n + 2
C.J Everett
1977
A density estimate for the 3x + 1 problem
Ivan Korec
1994
An Update on the 3x+1 Problem
Marc Chamberland
2003
The 3x + 1 Problem: An Overview
Jeffrey C. Lagarias
2010
Almost all orbits of the Collatz map attain almost bounded values
Terence Tao
2019