EXAMPLE
Start with 15
Since 15 is odd, multiply it by 3 and then add 1: This gives 46
Since 46 is even we divide it by 2: We get 23
Now 23 is odd, so we multiply it by 3 and then add 1: We find 70
But 70 is even, so we divide it by two to find: 35
which is odd, and we continue like this...
For how long?
No one knows! Really...but it will likely end with 1.
In our case, the number 15 gives the following sequence of numbers:
15, 46, 23, 70, 35, 106, 53, 160, 80, 40, 20, 10, 5, 16, 8, 4, 2, 1
... and there it is!