Here’s something interesting I discovered when I was developing a simple blur method.
Perfect squares of odd numbers minus one are multiples of 8.

For instance:
3 * 3 – 1 = 8 = 8 * 1
5 * 5 – 1 = 24 = 8 * 3
7 * 7 – 1 = 48 = 8 * 6
…
21 * 21 – 1 = 440 = 8 * 55

I wonder what’s at work here. I’ll have to check Sir Isaac Newton’s notebooks.