Collatz sequence

The Collatz sequence, also called the Hailstone sequence, is a sequence of numbers relevant to the Collatz conjecture, which theorizes that any number using this algorithm will eventually be reduced to 1. The conjecture's truth is supported by calculations, but it hasn't yet been proved that no number can indefinitely stay above 1.

Formal definition
To get a Collatz sequence from a number, if it's even, divide it by two, and if it's odd, multiply it by three and add one. Continue the operation on the result of the previous operation until the number becomes 1.

Pseudocode Example
function collatz(n) while n > 1 show n   if n is odd then set n = 3n + 1 else set n = n / 2 endif endwhile show n

Example of a Collatz sequence
Collatz sequence of 25:

25 76 38 19 58 29 88 44 22 11 34 17 52 26 13 40 20 10 5 16 8 4 2 1

External resources
Collatz conjecture on Wikipedia