## Plus Blog

August 11, 2014
We have set up our temporary headquarters in Seoul, South Korea! We are here to attend the International Congress of Mathematicians, a huge maths conference that happens every four years. We are particularly excited because we'll witness the the award of the We will be reporting live on the award of the medals, as well as a range of other prizes that will be handed out, and no doubt meet many fascinating mathematicians to interview. Stay tuned! Sunset over Seoul. |

August 7, 2014
Image © Oliver Labs. Our image of the week shows a beautiful surface with many singularities, constructed using computer algebra. The image was created by Oliver Labs, using the software The picture is one of the images that appear in the book 50 visions of mathematics, which celebrates the 50th anniversary of the Institute of Mathematics and its Applications. You can see previous images of the week here. |

August 7, 2014
Most people are aware of the fact that computers work using strings of 0s and 1s. But how do you write numbers using only those two symbols? To see how, let's first remind ourselves of how the ordinary decimal way of writing numbers works. Let's take the number 4302 as an example. The digit 4 in this number doesn't stand for the number 4, rather it stands for 4000, or 4 x 1000. Similarly, 3 doesn't stand for 3 but for 300 = 3 x 100, 0 stands for 0 x 10, and 2 stands for 2 x 1. So 4302 means 4 x 1000 + 3 x 1000 + 0 x 10 + 2 x 1. Similarly, 7396 stands for 7 x 1000 + 3 x 100 + 9 x 10 + 6 x 1. What do the numbers 1000, 100, 10 and 1, which appear in these expressions, have in common? They are all powers of 10:
1000 = 10 To write a number in decimal notation, you first write it as a sum of consecutive powers of 10 (with the largest power on the left) and then pull out the coefficients of these powers. We can do the same with powers of 2 rather than 10. For example, the binary number 110 stands for
1 x 2 And the binary number 10001 stands for
1 x 2 You can convince yourself that a binary number only consists of the digits 0 or 1: when you write a number as a sum of consecutive powers of 2, no other coefficients are necessary. This sorts out the natural numbers, but what about numbers that have a fractional part? To write a number between 0 and 1 in binary, you play the same game using powers of 1/2 instead of powers of 2. For example,
0.75 = 1/2 + 1/4 = 1 x 1/2 In binary, 0.75 is written as 0.11. The binary number 0.1001 stands for the decimal number
1 x 1/2 Easy! You can find out more about the |

July 31, 2014
Image © Tim Jones. This beautiful image shows details of the ceiling of the Sagrada Familia basilica in Barcelona, illustrating architect Antoni Gaudí's love of mathematical design. © Tim Jones. The picture is one of the images that appear in the book 50 visions of mathematics, which celebrates the 50th anniversary of the Institute of Mathematics and its Applications. You can find out more about maths and architecture here and about maths and art here. |

July 30, 2014
A perfect number is a natural number whose divisors add up to the number itself. The number 6 is a perfect example: the divisors of 6 are 1, 2 and 3 (we exclude 6 itself, that is, we only consider proper divisors) and 1+2+3 = 6.
If a non-perfect number were an animal, it might look something like this. If you play around with numbers for a while you will see why people have always been so fond of perfect numbers: they are very rare. The next one after 6 is 28, then it's 496, and for the fourth perfect number we have to go all the way up to 8128. Throughout antiquity, and until well into the middle ages, those four were the only perfect numbers that were known. Today we still only know of 48 of them, even though there are fast computers to help us find them. The largest so far, discovered in January 2013, has over 34 million digits. Will we ever find another one? We can't be sure — mathematicians believe that there are infinitely many perfect numbers, so the supply will never run out, but nobody has been able to prove this. It's one of the great mysteries of mathematics. You can find out more in Number mysteries. |

July 24, 2014
In the process of writing an article on curvature we got entirely distracted by making a geogebra worksheet showing the tangent, normal and osculating circle to any smooth function. The meaning and mathematics of all these terms is revealed in this article, but if you fancy getting your hands dirty yourself, have a play with the worksheet below. Please post your favourite function as a comment – the curvier and wigglier the better! You can use this geogebra worksheet to see the tangent, normal and osculating circle of any smooth curve you choose - just change the equation |