What is a good reference on the 3N+1 problem?

arithmetic/three.n.plus.one New

New entry, edited from material collected for the archive and not yet in a released version.

Problem

What is a good reference on the 3N+1 problem?

[ Editor: the 3N+1 (Collatz) problem asks whether repeatedly replacing
N by N/2 when N is even and by 3N+1 when N is odd always reaches 1,
whatever positive integer N you start with. ]

[ Editor: problem statement reconstructed from the postings. ]

Show solution

The reference suggested by nearly everyone who replied to a request for
an extensive bibliography on the 3N+1 problem is:

  J. C. Lagarias, "The 3x+1 problem and its generalizations,"
  Amer. Math. Monthly 92 (1985) 3-23.

-- JK