Bitesize has changed! We're updating subjects as fast as we can. Visit our new site to find Bitesize guides and clips - and tell us what you think!

Home > Maths > Algebra > Number patterns


Number patterns


Triangle numbers

Triangle numbers can be represented as a triangle of dots.

The triangle numbers are:

Triangle numbers represented by dots aligned to make equilateral triangles

What is the next triangle number after 21?


The next row of the triangle will have 7 dots. So the next number is

1 + 2 + 3 + 4 + 5 + 6 + 7 = 28

28 dot equilateral triangle


Number patterns activity

Follow the rules and try this activity!



Use your knowledge to help Spherox find his way home.

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.