I used three lolly sticks to make one small triangle: 

I added more lolly sticks to make four small triangles:

How many lolly sticks have I used altogether now?

I decided to add another 'row' of small triangles. 
Can you picture in your head what this will look like?
How many small triangles will there be?
How many lolly sticks will I have used in total?

Once you have had a think, you might like to check by making the pattern yourself, or by sketching it. 
You could click below to see what my pattern looked like.

I carried on adding rows of small triangles, and I found many patterns.

Have a go yourself! You could use lolly sticks or straws or..., or you could draw lines.