The problems in this feature introduce the idea of modular (or clock) arithmetic, and encourage you to explore the modular world. There are opportunities for noticing patterns and discovering some general rules which hold in this type of arithmetic.

You can build on these ideas when exploring our Public Key Cryptography Interactivity, and see how Public Keys are used to keep our personal information secure.

The last day for sending in solutions to our live problems is Monday 17 May.

Challenge Level

What happens if we change the rules and make the usual straight number line into a circle?

Challenge Level

Investigate what happens when we add or multiply numbers using modular arithmetic.

Challenge Level

Can you find a way of predicting the value of large square numbers with the help of our power modulo calculator?

Challenge Level

How many numbers are there less than $n$ which have no common factors with $n$?

An introduction to coding and decoding messages and the maths behind how to secretly share information.

Here's a chance to simulate sending secret messages and trying to decode them.

An introduction to some beautiful results in Number Theory.