9 is an experimental error

As many will know, at the start of episodes of the Travels in a Mathematical World podcast I give a number fact. My intention at the start was that I would also point out when numbers are prime, buoyed on by enthusiasm for prime numbers.

In episode 9 of the Travels in a Mathematical World podcast, the first of two in which Dr. Adrian Bowyer talks about his fascinating career, I make an extraordinary claim: 9 is prime. There’s a joke along these lines:

How to prove that all odd integers greater than or equal to 3 are prime.

Mathematician: 3 is a prime, 5 is a prime, 7 is a prime, and by induction – every odd integer higher than 2 is a prime.
Physicist: 3 is a prime, 5 is a prime, 7 is a prime, 9 is an experimental error, 11 is a prime. Just to be sure, try several randomly chosen numbers: 17 is a prime, 23 is a prime…
Engineer: 3 is a prime, 5 is a prime, 7 is a prime, 9 is an approximation to a prime, 11 is a prime,…
Statistician: 100% of the sample 5, 13, 37, 41 and 53 is prime, so all odd numbers must be prime.
Programmer: 3 is prime, 5 is prime, 7 is prime, 9 will be fixed in the next release, …

and so on. There are more of these all over the web, including a substantial list on gdargaud.net.

So I need to apologise for and retract my bold claim. As for an explanation, I do not know what happened! There is also an issue that I say “excluding 1, for which the case is trivial, 9 is the smallest number which is equal to the sum of the digits of its square.” Whereas the entry in trusty Number Gossip tells us 9 is “the only number (except one) which is equal to the sum of the digits of its square” (emphasis added). Now, my statement is not wrong, per se, but strange to have added the extra clause (although my weaker claim is easier to prove by exhaustion, I suppose). I struggle to remember where I got the result from – the reference I give in the show notes for episode 9 points to thesaurus.maths.org, where the result is not claimed.

I think we might just have to assume I switched off my mathematical brain for that week. Anyway, I am grateful to an anonymous poster on the show notes for episode 9 of the Travels in a Mathematical World podcast for pointing out my error. I wonder if the first 294 people who downloaded the episode: (a) didn’t notice; (b) noticed but didn’t tell me; or, I suppose, (c) downloaded the episode but didn’t listen to it. Any of these leaves me a little disheartened.

This also led me to look at the other prime episodes and realise my original intention of noting prime number episodes is erratic at best. Quite apart from the erroneous, I state the fact for episodes 2, 3, 7, 13 and 17 but am guilty of omission in episodes 11 and 19. Episode 23 will be the next maths news episode and we will see if I remember to note the fact.

Podcast Episode 21: History with Noel-Ann Bradshaw, Turing

These are the show notes for episode 21 of the Travels in a Mathematical World podcast. 21 is the number of squares in the unique smallest simple squared square. You can see the square with some more information on the page about its use as the logo of the The Trinity Mathematical Society at Cambridge. There is more information on squaring problems at squaring.net. More about the number 21 from Number Gossip.

In the regular Maths History series, Noel-Ann Bradshaw of the University of Greenwich and also Meetings Co-ordinator of the British Society for the History of Mathematics talks about the life of Alan Turing. You can read a biography of Turing at the MacTutor History of Maths Archive and there are a large number of links to further reading on the Alan Turing Wikipedia page.

You can find out more about my work with the IMA by following me on Twitter, reading this blog and visiting www.ima.org.uk/student.

Who watches the listeners?

Web site logs are compelling and addictive. I have just got lost in the logs for the blog and podcast for half an hour before my phone beeped and drew me back to the real world. Anyway, I am interested to see the following websites sending people to this blog and the Travels in a Mathematical World podcast.

Mr T’s Standard Grade Maths Blog

This is the blog of a teacher, Mr. T, aimed at his students and has excited me greatly for two reasons – First, the link to the podcast comes in a post entitled “Exciting new links!“; Second is the text that immediately preceeds the link

As promised here are a couple of interesting links the first is the blog mentioned in class which includes the podcasts of discussions with interesting mathematicians. Be warned some of the maths is quite high powered but very interesting nonetheless:

Did you notice “mentioned in class”? Very exciting!

KTN for Industrial Mathematics

There are people visiting from the post on the noticeboard of the KTN for Industrial Mathematics, who are involved with linking research with business.


We have hits coming in from condron.us, which seems to be a site which flashes different blogs at you for a few seconds each until you see one you want to read. I’m not sure if this is people reading it then, or just waiting the four seconds until the next blog!


This is a page of interesting looking links which includes a link to the podcast.

Paul Shepherd’s website

Paul was in episode 14 of the Travels in a Mathematical World podcast and links to this from his page on Public Understanding of Mathematics.


We are linked in the IMA entry on Wikipedia! Fame and fortune beckon… The podcast gets a mention in the Publications section of the page (with a link to the Travels in a Mathematical World entry that doesn’t currently exist; Hint, anyone?) and the link is in the External Links section.

University websites

I am glad to see the blog and podcast are linked to, sometimes along with the IMA Careers Advice leaflet and Maths Careers website, from the following universities: Bath, Brunel, Dundee, Queen Mary (London) and Warwick. I do not know if these are the only universities that link to the blog or podcast, but these are the ones that are appearing in the web logs.

Podcast Episode 20: Choi-Hong Lai, Fluid dynamics

These are the show notes for episode 20 of the Travels in a Mathematical World podcast.In a game of chess both players have 20 first moves from which to choose. More about 20 from Number Gossip.

For episode 20 I visited the University of Greenwich and met Professor Choi-Hong Lai, who talked through some applications of fluid dynamics. The Wikipedia page on fluid dynamics seems fairly readable as an overview. If you’re in a university your university library will hold introductory books on fluid dynamics. You can find further information about Choi-Hong’s research on his website.

You can find out more about my work with the IMA by following me on Twitter, reading this blog and visiting www.ima.org.uk/student.

100 posts later, who is Peter Rowlett?

This is my 100th post, yipee! I’m going to take the opportunity to review my current activities as these have changed recently.

In an adjustment to my working this week, I started at the University of Nottingham‘s School of Mathematical Sciences as an elearning and web chap. I remain University Liaison Officer for the Institute of Mathematics and its Applications (IMA). My PhD, in elearning in mathematics, is currently suspended to allow me to work full time for one year to bolster the finances. I do though remain as a lecturer at Nottingham Trent University (NTU), teaching a level 2 skills development module this semester, although I do not intend to take on any more teaching after this – the 6.5 day week is not so great! I also remain registered for a Postgraduate Certificate in Higher Education (PGHCE), a 60 credit Masters-level induction course for new lecturers at NTU. If all continues to go well I will graduate from this at the end of the academic year.

In other good news, I received a letter on my return from Scotland last week that I have been successful in my application for full membership of the IMA, Member (MIMA) where previously I have been Associate Member (AMIMA) since 2005. My mum asked “Does that mean you don’t have to pay any more?” Erm, no, it means I have to pay more. “Oh, does it mean you get more letters after your name?” Erm, no, it means I get one less letter after my name. I don’t think she got it!

All degrees are not created equal

I saw a really interesting piece on BBC Breakfast this morning in which the claim was made that there are now too many graduates entering the jobs market and that graduates of many degrees are not finding graduate jobs as a consequence. This interested me particularly because of an incident earlier in the week. I was asked by a student at one of my careers talks in Scotland why, given what I was saying about what an excellent degree mathematics was for so many career choices, numbers of students taking mathematics was falling. Firstly I said I thought we are starting to turn that particular tide, with good inititatives and a rise in numbers (with maths rising above the general rise). Secondly I said I felt there was a lack of understanding among school students looking to take degrees of the relative value of different degrees, with students thinking maths is a difficult choice of degree subject and not realising the extra value that it has for their graduate prospects.