## Carnival of Mathematics #99

Welcome to Carnival of Mathematics #99. Wikipedia provides some nice trivia about the number 99.

99 is the ninth repdigit, a palindromic number and a Kaprekar number. It is the sum of divisors of the first eleven positive integers.

99 is the sum of the cubes of three consecutive integers:

99 = 2^3 + 3^3 + 4^3

And, I personally like that 99 is the difference of two squares: 99=10^2-1^2.

Now, onto the carnival articles.

John Cook shares Recognizing numbers. For Python users, SymPy is a symbolic math package that "takes a floating point number and tries to simplify it: as a fraction with a small denominator, square root of a small integer, an expression involving famous constants, etc."

Mike Thayer, in Algebra and Geometry, asks this question: "I teach algebra 1, to 9th and 10th graders, mainly. I also teach geometry to the same age group. I'm wondering the following: Why is it that the conversations in geometry are so much more interesting, generally?"

Peter Rowlett takes a break from PhD preparation to explore Ox Block probabilities. "I'm not blogging much in the run up to my PhD thesis deadline, but my curiosity got the better of me with this one. Having seen (via Twitter) that it was being played at a Maths Jam, I bought an old game called Ox Blocks, which offers “Noughts and Crosses[/Tic Tac Toe] with a novel twist”. Here, I investigate the probabilities of rolling an unusual die."

Thomas Woolley writes Egg shells to turtle shells. "No matter how you initially orient the gömböc it will always wobble and rotate itself to finish standing upright. Importantly, the gömböc is made of only one material, so its density is uniform. Mathematically, the gömböc is known as a mono-monostatic body. This simply means that it has exactly one stable and one unstable equilibrium point."

Tony, a university maths professor in London, in My favorite equation considers whether there's a more interesting formula than Euler's formula. "So McKay's formula may not be as immediately beautiful as Euler's, but it has something of the same spirit (and perhaps even importance). It demonstrates a very deep connection between group theory and modular forms; it's mysterious and hard to understand, and it's inspiring important mathematics. And it says a lot about the serendipity which lies behind insights even in a subject as apparently logical and rigorous as mathematics."

Simon Gladman wonders what pendulum waves might sound like in The Sweet Sound of Pendulum Waves - in Glorious Stereo! "I had a little play with Pendulum Waves the other day and since then I've been wondering what sort of sound they would make if I played a tone as each pendulum reached its apex."

Have you ever wondered Why are determinants defined the weird way they are? If you've ever wondered why, whether or not you've studied linear algebra, you might enjoy this article. It'll give you some great material for your next party conversation!

Yao-Hong Kok is a Master's student studying control theory. Math, Control Theory and Two Issues invites interested parties into a discussion. "Control theory is one of those fields that requires a lot of mathematics. I have been in the field for roughly 2 years now and I have realized that they are 2 big issues within control theory, namely: (i) identity of a control engineer/theorist, and (ii) stagnation of fundamental theory advancements. In this post, I would like to relate mathematics to the above issues and perhaps generate some discussions."

Maria Droujkova shares Math dreams meeting May 20, 2013. "Curriculum developers' elephant in the room is a simple question: "Who wants that stuff, anyway?" We decided to ask parents what do they want for their kids, in math. Deep is the chasm between what parents want, and what existing curricula provide..."

Shecky Riemann, inspired by Martin Gardner's passing to start his blog, writes Remembering... Gardner three years after his death. "Not to take anything away from our Veterans, but this is a math blog, and I'll use the opportunity of Memorial Day to once again remember Martin Gardner, whose death just over 3 years ago inspired me to start this endeavor (with no idea it would still be up-and-running 3 years later!!)."

Herminio Lopez examines an interesting puzzle in A black (and red) hole. "Thanks to a prize consisting on the proceeds of a football match, we learn about some numbers that attract the others, which can't escape from them. Mathematical sequences which lead to mathematical black holes."

In Demystifying the Möbius, Burkard and Marty take readers on a nice journey through the many twists and turns that one can take with these paper treats.

Predicting Sums is a fun article at Grey Matters. It shows a nice math trick one can perform with a little knowledge of digital roots (aka nine's complements).

Math Munch is a great blog for children of all ages that describes itself as "A Weekly Digest of the Mathematical Internet." Their latest edition is Solitons, Contours, and Thinking Sdrawkcab. Check it out if you've not yet discovered this blog.

The Aperidical is another of my favorite blogs. They describe themselves as "a meeting-place for people who already know they like maths and would like to know more. It was begun by Katie Steckles, Christian Perfect and Peter Rowlett as a shared blogging outlet and grew out of our desire to have a place on the web where we could keep up to date with what’s going on elsewhere, and to share the mathematical things we do." You might also recognize Aperiodical as the stewards of this Math Carnival. Christian authored this fun piece, Integer sequence review: A000959.

If you've ever wondered what math and the meaning of life were related, check out 42 at Calculus Humor. This article deserves to go viral. Really.

Finally, I'll share one of my own favorite recent articles, Ken Fan: Inspired by Math #29. It's a podcast interview where Ken and I had a nice informal chat without much preparation before-hand.

The next carnival, #100, will be posted in July and hosted by Richard at Simple City. More information about the Carnival of Mathematics, and a submission link, is posted at the Aperiodical site.

## I’m hosting Carnival of Mathematics #99

I'll be hosting the next Carnival of Mathematics. Please check out this URL to learn more about the carnival, to vist past carnivals, or to submit your blog article for #99. Submission deadline is 6/1/13.

## 81st Carnival of Mathematics

Welcome to the September 2, 2011 edition of carnival of mathematics.

This is the 81st edition. In the tradition of the Carnival of Mathematics, we provide trivia on the number of the edition.

- 81 is 3^4 and also 9^2.
- The awesome card get, Set, contains 81 cards.
- 81 is the square of the sum of its digits. Thanks to this site.
- 81 is a heptagonal number and a 28-gonal number.
- There are 81 stable chemical elements.

Some more trivia about the number 81 appears here.

That concludes this month's Carnival of Mathematics. Oops, we've not mentioned our submissions. There are lots this month. Here they are ...

**Mike Croucher**, owner of the Carnival of Mathematics, presents A retrospective of 4 years of mathematical articles at WalkingRandomly. Happy Birthday, WalkingRandomly! I'm a big fan of Mike's blog and I discovered a bunch of neat articles among his most popular.

**Mike Croucher** also nominated these two articles:

## Mathematica and Multimedia Blog Carnival #11 is up!

Mathematica and Multimedia Blog Carnival #11 is up at Love of Learning Blog.

## Carnival of Mathematics #77 posted

Carnival of Mathematics #77 has just been posted at Jost a Mon.

## Mathematics and Multimedia Carnival #4

Welcome to the fourth edition of the Mathematics and Multimedia Blog Carnival.

* Note: All images in this post are from Wikipedia.

The Number 4

- Four is the smallest composite number, its proper divisors being 1 and 2. Four is also a highly composite number. The next highly composite number is 6.
- Four is the second square number, the second centered triangular number.
- 4 is the smallest squared prime (p
^{2}) and the only even number in this form. It has an aliquot sum of 3 which is itself prime. The aliquot sequence of 4 has 4 members (4, 3, 1, 0) and is accordingly the first member of the 3-aliquot tree.

The Entries

(1) Jacqueline Barbour presents Teach addition so your child can remember it posted at Pain Free Math. A nice approach to using very simple props and a number line to teach addition and subtraction.

(2) Milo Gardner presents Ahmes Papyrus, New and Old Classifications posted at New and Old Ahmes Papyrus classifications,. The history of Western mathematics includes 200 rational number based problems recorded in Egyptian (2050 BCE to 1550BCE) unit fractions. The RMP is sometimes called Ahmes' Papyrus, named after its scribe. The hieratic text described 87 problems: 20 arithmetic, 10 algebraic, 10 geometric, 46 economic (weights and measures) and one mod 7 recreational problem known in the medieval era as "Going to St. Ives". Forms of unit fraction arithmetic remained in use until 1454 AD, the latest text was Fibonacci's Liber Abaci, Latin writing Europe's arithmetic book from 1202 AD to 1454 AD, and fully replaced by base 10 decimals by 1585 AD.

(3) Ed Pegg Jr presents Happy Vampire Day posted at Wolfram Blog. "October has a rather special day—10/05/2010 is a vampire date, since 10052010 = 5001 × 2010. The next two 8-digit vampire dates are 10/05/2064 and 10/19/2248. As a puzzle, try to figure out how to rearrange their digits into two 4-digit numbers, which have a product of the original number."

(4) zar presents Dimostrazione senza parole (demonstration without words) posted at Gli studenti di oggi. Zar's blog is written in Italian, but this particular post is "without words."

(5) Erlina Ronda presents GeoGebra and Mathematics: Investigating coordinates posted at Keeping Math Simple.

(6) John Golden presents Fraction Multiplication posted at Math Hombre -- A Geogebra visualization for multiplying fractions, along with a novice screencast and a discussion of embedding geogebra in a blog.

(7) William Emeny presents A sequences alternative to ‘how many matchsticks’ posted at Great Maths Teaching Ideas. "Make lessons on sequences much more interesting by adding context! Use sequences to analyse skyscrapers!"

(8) David Wees presents The Death of the Amateur Mathematician posted at Professional blog | 21st Century Educator. This is a discussion about what is happening in the field of education today.

(9) John Cook presents Variations on factorial! — The Endeavour posted at The Endeavour.

(10) Rebecca Zook presents How To Multiply Binomials Using a Box! posted at Triangle Suitcase - Rebecca Zook's Blog About Learning. "Many people find this "box" method for multiplying binomials more intuitive than foiling. I created this series of short videos to share this idea with other math teachers and students."

(11) Guillermo Bautista presents Mathematics in Microsoft Office « Mathematics and Multimedia posted at Mathematics and Multimedia. This is an article on integrating mathematics to office suites.

(12) Last but not least, I submit my own review of The Mystery of the Prime Numbers. This is an amazing book, with great illustrations that looks like a children's book but will appeal to anyone who wants to dive deep into simple ideas.

This concludes our third Carnival of Mathematics and Multimedia. The next Carnival will be hosted at the Math Hombre blog on November 8th. Submit your entries here.

Past Carnivals

Please Help Promote the Carnival

The Math and Multimedia Carnival is a baby carnival, so please promote this Carnival in your blogs.

## Reminder: submissions due for Carnival of Mathematics and Multimedia

Just a reminder that your submissions are due Friday October 8 for the next Carnival which I'll be hosting the following Monday. More information about the Carnival is here.

Please submit your blog articles via the official submission form.

## Mathematics and Multimedia Carnival #3 posted

The Mathematics and Multimedia Blog Carnival #3 has been posted. Starting next months the Carnival will travel. I'll be hosting #4 (a number that's easy to say something about.)

Please submit your articles using the official form.

## Couple of carnivals and a clever clock conundrum

Two Math carnivals have recently been published:

- The 68th Carnival of Mathematics at +plus magazine
- The 2nd Mathematics and Multimedia Blog Carnival at the Mathematics and Multimedia Blog.

Now, here's a challenging adaptation of a problem I recently discovered. I won't reveal the source till later to not give away the problem.

There's something interesting about the time 2:26 and other times of the day. This interesting thing can be seen over 100 times per day. What is the property and exactly how many times does it occur in a day?