# Carnival of mathematics 152

We round up some of the last month’s top mathematical posts from around the internet

Welcome to the 152nd Carnival of Mathematics, the monthly round up of maths blogs organised by The Aperiodical. Next month’s Carnival will be hosted by Ganit Charcha. You can submit items for next month here.

It’s been a good month for maths blogging, and here we feature posts about a wide range of topics: from bricklaying and Smarties to cryptography and (of course) Christmas. But, before we get going with the blog posts here are a few facts about the number 152:

• 152 is the sum of 4 consecutive primes (31 + 37 + 41 + 43).
• It is divisible by the total number of divisors it has, and hence can be called a refactorable or tau number.
• Its a film! A 2006 Japanese horror film to be precise. Is 152 really scary? Is maths really scary?

It’s been a busy month, which has included this year’s annual MathsJam Gathering. There have been many posts explaining just how great MathsJam is, including Rob Low’s summaries of all the talks, Colin ‘IceCol’ Beveridge and Dave Gale’s latest Wrong but Useful podcast, and this post by MathsJem. We here at Chalkdust even posted our own reflections on the event.

Inspired by a MathsJam talk, Rob Low wrote this post about Russian peasant cryptography, applying the idea behind the Russian peasant multiplication method to RSA.

Matt Parker’s infamous failed attempt to find a magic square filled entirely with square numbers. Image: Brady Haran, CC BY 3.0

It’s been a month full of unexpected connections: Colin Beveridge noticed an interesting connection between the Parker square and a dodgy tweet about prime numbers; and Lucy Rycroft-Smith interviewed a builder and answered the question every maths teacher is tired of: “when will I ever use this in real life?”

Vi Hart posted this video about Smarties. As well as showing you lots of fun bits of maths, this video will also teach you that Smarties in America are not the same as Smarties everywhere else.

Mark Dominus made an interesting observation about how late you will be if you leave home two minutes late.

A Koch snowflake.

By now, you’ve probably noticed that it is now December and everything is turning more and more Christmathsy. To get you in a festive mood, we recommend reading Evelyn Lamb’s Scientific American post on Koch snowflakes, and following Clarissa Grandi’s instructions for making some origami snowflakes.

If puzzles are more your thing, you’re not too late to catch up with the mscroggs.co.uk advent calendar, or enter the first Chalkdust Christmas conundrum. We also recommend having a go at the following recently posted puzzles:

### Weights by Daniel Griller

A balance and a set of metal weights are given, with no two the same. If any pair of these weights is placed in the left pan of the balance, then it is always possible to counterbalance them with one or several of the remaining weights placed in the right pan. What is the smallest possible number of weights in the set?

### Right angled triangles by Danesh Forouhari

How many right angled triangles are there whose sides all have integer length and have one side of length 120cm?

TD is an undergraduate at UCL who actually understands the 1967 James Bond spoof Casino Royale, starring David Niven, Peter Sellers, Woody Allen, and Orson Welles as Le Chiffre.

Matthew is a postdoctoral researcher at University College London. He hasn’t had time to play Klax since the noughties, but he’s pretty sure that Coke is it!

• ### Crossnumber winners, Issue 17

Did you solve it?
• ### Crossnumber winners, Issue 16

Did you solve it?
• ### Prize crossnumber, Issue 16

Can you solve it?
• ### Cryptic crossword, Issue 16

Can you solve it?
• ### Crossnumber winners, Issue 15

Did you solve it?
• ### My favourite LaTeX package

The Chalkdust editors share some of their favourites