So here we are on December 23, 2015, the 93rd edition of Math Teachers At Play! As per tradition, what’s so fascinating about the number 93?

First, it’s a prime number! No. Wait, that’s clearly false. So 93 is not a prime number. But that’s not very fascinating. Aha! But 93 is a semi-prime! since \(93 = 31 \times 3\). Even more interesting is that 94 and 95 are semi-primes. So a question is, is there another triplet of positive integers that are also semi-primes? It’s a good question to ask your students!

What’s cool about 93 being a semi-prime is that 39 is also a semi-prime since \(39 = 13 \times 3\). So a little fun numerology is that 93 is just 39 written backwards and so its prime factorization! Are there other semi-primes like this? For example, 15 and 51 are semi-primes, but \(15 = 5 \times 3\) and \(51 = 17 \times 3\). So 15 and 51 don’t work as well as 93 and 39. There is at least one other pair that behaves like 93 and 39 in its prime factorization. Which is it? Another fun puzzle for your students!

Ok, now for link fest.

Our first two submissions come from @LthMathematics about (a) Wrapping Presents Like A Mathematician! Check out the videos!! and (b) Christmath Trees!

Our next submission is from @DrBennison: An A-Level Calculated Colouring. In his own words

In the UK most students will have done a calculated colouring at some point in their time at secondary school (they are very popular for end of term lessons/cover lessons etc, in part due to their inclusion in the 10Ticks worksheet bundles that many schools subscribe to). My A-Level/ KS5 (I think Grade 11 & 12 in the US) classes have been asking for a while for an A-Level calculated colouring so I decided to make one for them. 100 questions that identify regions in a seasonal picture, the answers of which determine the colour to be used.

Incidentally, Tom has been on a roll on Twitter. You should check out the Maths Book Journal Club when you get a chance. It is also a Twitter chat! Just message @DrBennison for details.

Another fellow Twitter math friend, Stephen Cavadino (@srcav) submits How are we questioning our students? with commentary

A post looking at a journal article on the question types asked upon leaving school in the UK and at undergraduate degree level, and what it can tell us about questions we ask.

Fellow math web comic Twitter friend, Gregory Taylor (@mathtans) shares his personified math web comic Any Q Bars. This is a multi-parter so make sure to read the following ones!

Daisy Fryer reviews some math addition games for those who may want to take a modern approach to arithmetic practice.

Denise Gaskins, organizer of #MTaP, shares a first post in a series of posts to come about understanding school math. Check out the post as it will take you through the reform pendulum that has plagued (math) education. On a similar note, Caroline Mukisa (@mathsinsider) gives some advice on conquering your child’s math anxiety.

But why is there math anxiety? Heck this is the Math Misery blog! For my own submission check out Math misery? I think I know why.

<EDIT 12/23>John Golden (@mathhombre) sends us this post about holiday wrapping!

Finally, here is a Christmaths puzzle for you: “ALL I DO: SIN COS TAN” Who Am I? Leave a comment with your answer and find out this Christmas!