That's a great read. I don't understand the prime number part though:

> 3599 = (3600 – 1) = (602 – 12) = (60 – 1) (60 + 1) = 59 times 61. Not a prime number.

Where does the (602 - 12) come from? Can someone explain that to me?

Also, use a leading space to keep things out of your bash history.