**Click here** to see what the problem calls
for.

**Did you get 1, 5, 13, 27 so far? Yes. How many triangles
when there are five levels? 10 levels?**

Take a look at the number of triangles when there are five levels and when there are ten levels:

**How do you verify your sequence?**

The way my kids would probably verify their sequence is by actually working the problem out by using the skill of drawing to enhance their creative side.

**Is there a general formula for n levels?**

Tn ....T(n-1)

**Proof?**

We do not have total proof just yet.

Comments:

Recognition of the sequence of **triangular
numbers** is useful.

Hint: Count the number of triangles of each size in two parts:

those pointing up and those pointing down.