Longest Collatz sequence

Created on Jan. 18, 2017 by Julien Palard

The collatz sequence goes like this:

• Start by any number greater than zero.
• If your number is even, divide it by two.
• If your number os odd, multiply by three and add one.

For example, starting by 10 we have:

10 → 5 → 16 → 8 → 4 → 2 → 1

Write a function, named collatz_length, given a number the function return the length of the sequence before reaching 1, for example:

>>> collatz_length(10)
6

Because it takes 6 steps (6 → in the previous example) to reach 1.

Advice

Have fun.