1, 1, 2, 3, 5, 8, 13, 21, 34

Do you see why?

We added the first two numbers, 1 + 1 and got the third number, 2...

To get the 3, we added the two number that came before it, 1 + 2...

To get the 5, we added the two number that came before it, 2 + 3...

To get the 8, we added the two number that came before it, 3 + 5...

To get the 13, we added the two number that came before it, 5 + 8...

To get the 21, we added the two number that came before it, 8 + 13...

So...

We get the 34 by adding the two numbers before it, 13 + 21.

And it goes on and on and on!

This is a very famous sequence (list of numbers) called the Fibonacci Numbers.