If the square root of +1 is both +1 and -1, then what is the square root of -1?
The Imaginary Number
Georg Cantor defined infinity as the size of the never-ending list of counting numbers.
Another Five Numbers
The Number Four
Are 4 colours enough to paint any map, so neighbouring countries have different colours?
The Number Seven
Are 7 shuffles sufficient to achieve a good degree of randomness in a deck of 52 cards?
The Largest Prime
Can large prime numbers be used to form the basis of more secure encryption codes?
Is the 'face-centred cubic lattice' the most efficient way of stacking spheres?
When 3G phone licences were sold, game theory was used to boost proceeds for the Treasury.
A Further Five Numbers
One - The most popular number
One is the most popular number, as it appears more often than any other number.
Two - At the double
Doubling is a form of exponential growth, which appears in population growth and inflation
Six degrees of separation
Six is often treated as 2x3, but has many characteristics of its own.
G - The number that defines the universe
Newton's equation of gravity includes a number G, indicating the strength of gravitation.
1729 - The first taxicab number
1729 is the smallest number you can write as the sum of two cubes, in two different ways.
The young climate change activists persuading us to change our behaviour
The Smart Consumer Podcast with Jess Quayle and Lydia Thomas
The Guilty Feminist, Edd China, Aladdin
Nicola Meighan chats to Deborah Frances White, host of the Guilty Feminist podcast.
Google's blow to Huawei
The Chinese giant's phones face uncertainty after Google stops providing apps and its OS.
5 - R.E.S.P.E.C.T.
Suspicion and betrayal: in this rhino war, trust is nowhere.
How YouTube decides what you should watch
The secrets of YouTube’s powerful algorithm in the words of a former company insider.