BlameThePixel!

Just whatever seems to interest me at the point in time that I heard about it or figured it out.

Spoiler (Click to Expand)

It's all simple pairing. Look at the first and the last number in each of them. The first one has you multiplying 9 by 111111111. The second one has you multipying 999999999 by 1. It works because each number is being multiplied to the same number of whole places.

You can even mix up the appearances of the numbers, like this:

5 * 66 * 444 * 7777 * 33333 * 888888 * 2222222 * 99999999 * 111111111

The rules are:

1) Each number from 1 to 9 MUST be used ONE time.
2) Each length from 1 to 9 MUST be used ONE time.
3) Each individual number must consist of nothing but whatever number is chosen for it.
4) Rather obvious, but you can't have more than 9 terms.

It's useful if you're on Jepardy