Question have arrived, a very nice investigative piece on what numbers can be written as a difference of two squares. Had some fun playing with this problem on the last lesson on Friday:

Which integers can be expressed as a difference of two squares (x²-y²), and which of these can be expressed as a difference of two squares in more than one way.

Took less than an hour to derive a convincing argument. It's always fun to introduce modulo arithmetic. Particularly square numbers and modulo 4.