I Solved The Mystery!!!! :D

*Looks around expectantly to see if anyone claps or cheers*

*Nothing Happens*

Aww...

A load of Year 6 students in a classroom. A bald teacher talks to them. The students get on with their task.

A boy and I take it in turns to write a short sequence of numbers on a mini whiteboard. Then the person not writing then writes more figures that correlate with the pattern.

He writes, 200, -200, 200, -200, 200, -200...

I write, ...200, -200, 200, -200, 200, -200...

Later on in the lesson, we cover the nth term.

Ever since then, I have thought back to that sequence, wondering whether there was a way to express the general pattern of the sequence. But not enough to use Google.

And today, I found it at long last.

Now are you happy?