Calculator Tricks 5 By Brian Carruthers HERE’S ANOTHER TEASER FOR YOUR STUDENTS. HOPE THEY HAVE FUN. REGARDS, BRIAN.

The 421 Loop Pick a whole number and enter it into your calculator. If it is even, divide by 2. If it is odd, multiply by 3 and add 1. Repeat the process with the new number over and over.

What happens?

The sequence always ends in the “loop” 4…2…1…4…2…1…

For Example: Let’s Start with 13 13 is odd, so we multiply by 3 and add 1. We get 40. (13 x 3 = 39 + 1 = 40) 40 is even, so we divide by 2 . We get 20. (40 / 2 = 20)

20 is even, so we divide by 2 and get 10. 10 is also even, so we divide by 2 again and get 5.

5 is odd so we multiply by 3 and add 1. We get 16. 16 is even, so we divide by 2 and get 8. 8 is also even, so we divide by 2 again and get 4.

4 is even, so we divide by 2. We get 2. 2 is even, so we divide by 1 and get 1. 1 is odd, so we multiply by 3 and add 1. We get 4. 4 is even , so we divide by 2. We get 2. 2 is even, so we divide by 1. We get 1.

And so we begin the loop 4…2…1…4…2…1…

Now what did you think of that?