It's explained in the program.
'Start with any number, and the sequence will always end in 1'
Start at any positive integer.
If it's even: divide by 2.
If it's odd : multiply by three and add 1.
Repeat this process over, and eventually you'll end up with 1.
There's no proof of this conjecture, so there's actually about £5000 up for grabs for anyone who can prove it to be true!