Directed graph showing the orbits of the numbers less than 30 (with the exception of 27 because it would make it too tall) under the Collatz map.

For a larger graph containing only odd numbers, see Image:Collatz-graph-300.svg.

Created with Graphviz, with the help of this Python program:

dotfile = file('collatz-graph.dot', 'w')

limit = 30

def f(n):
  if n % 2 == 0:
    return n / 2
  else:
    return 3*n + 1

explored = set([1,27])

dotfile.write('digraph {\n')

for n in range(2, limit):
  while n not in explored:
    dotfile.write(str(n) + ' -> ')
    explored.add(n)
    n = f(n)
  dotfile.write(str(n) + ';\n')

dotfile.write('}\n')

This work has been released into the public domain by its author, I, Keenan Pepper. This applies worldwide. In some countries this may not be legally possible; if so: I, Keenan Pepper grants anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law.