# Carnival of Mathematics 98

## May 2013

Hello!

First of all, regular readers confused by suddenly arriving at #98 in a series you’ve never seen before should read this page to find out what’s going on. In short, it’s a monthly collection of user-submitted maths blogging, hosted by a different blog each month.

Everyone else, welcome to the 98th Carnival of Mathematics! As per tradition, here are some facts about the number 98:

• 98 is 77 in base 13, and also 72+72. (This sounds impressive but all numbers of the form 2n2 do that in base 2n−1.)
• 98 is a Wedderburn-Etherington number, which is to say the number of weakly binary trees you can draw with a given number of nodes. The first three such numbers are 1. Then it grows. Fast.
• 98 is a nontotient. (Don’t Google that. Trust me.)

## Maths and things

Patrick Honner has been given a speeding ticket and has used maths to prove that he definitely did the crime for at least a moment. It seems unlikely that either the cops or a judge has thought it through this far, though, so it might be worth arguing the toss. It’s worked before.

Tallys Yunes has devised an alternative set of times for microwaving food such that the ten digits are used roughly equally. I suppose in theory it could help protect your microwave from wear and tear, but really it’s delightfully pointless. My old microwave would accept times like 2:90, so maybe we could take this work even further…

Niles Johnson has blogged a gallant attempt to draw some shapes that presumably live in 8-dimensional space. Since my grounding in such things extends basically to having nearly completed Antichamber, I’m afraid I don’t fully understand it.

Stijn Oomes submitted a post on ‘rational trigonometry’ which is rather nice maths. I can’t see the use for it, but then, when has that ever made maths worse?

Richard Elwes has blogged about totients, handily explaining what “nontotients” are for anyone who obediently didn’t Google them earlier. The formula for finding them quickly is neat — and sort of obvious in retrospect so maybe try to find it before he tells you.

Wolfram’s blog has a good writeup of the Ramanujan Gap recently filled using their software. The Gap is a handful of missing solutions from Ramanujan’s old notebook. It has some nice 2D colour graphs in it too.

Lastly, here is a post by Mohammed Ladak about how intuitive and obvious the rules of Set are, which makes our attempts to explain it at MathsJam all the more pitiful.

## Resources, books and so on

Colleen Young has found a nice set of stats resources, and Justin Lanier has found some more general-interest ones including a website for playing the Four Fours game (and variants thereupon). Frederick Koh has sent a quiz about vectors and has some others on the site so they might be useful for anyone learning such things.

Colin Beveridge tells us about the Mathematical Ninja’s ten favourite numbers, and Christian Perfect sent in a blog by Adriana Salerno who has found x in a museum.

Lastly, Katie sent me a post by Mr Reddy with photos of all the things in his Maths Cupboard. It’s best played as a sort of maths-nerd version of the Conveyor Belt round from the Generation Game.