The Carnival of Mathematics is still going strong. This round – #76 – is hosted over at Walking Randomly and has, as usual, something for everyone, including a post from one my favorites: Language Log. (Yes, they use math there. Fairly often, in fact.) Go check it out, and while you’re at it, contact Mike if you’d like to host one.

## The Carnival Lives!

April 10, 2011## The Difference

April 9, 2011## Time to Fail!

April 8, 2011We luv us some failblog (regular or decaf), particularly on a Friday. Lately they’ve had a bunch of math fails, where “lately” means “since the last time we posted from there” and “bunch” is closer in number to “I bought a bunch of bananas” than “I have a bunch of papers to grade”. So without further ado, here are some favorites.

There’s trouble with dates:

and trouble with money:

and lots of trouble with percents:

Apparently, as Barbie once said, math is hard.

## Twelves

April 6, 2011The number 1729 has a right to be proud : it initially had only a small role on a taxicab in England but its super-power of being the sum of two positive cubes in not one but **two **ways (1^{3}+12^{3} and 9^{3}+10^{3}) led to a big break in a Feature Story starring GH Hardy and Srinivasa Ramanujan, with follow-up appearances for years to come on the likes of *Futurama *and *Proof*. So, you know, yay 1729.

But lest this Hardy-Ramanjuan number get too boastful, it’s not the only sequin at the Oscars. Its neighbor, that unassuming 1728, turns out to be an interesting character in its own right.

The origin of this is in the dozen. Although ten is a pretty natural base to use, in the sense that a lot of cultures break numbers up by tens in some form, it’s not the only possibility. We have not only a special word for 12 (dozen), but a special word for 12^{2} (gross), which suggests that our language carries hints of a Base 12 system. And that leads to the question: is there a special name for 12^{3}?

There is! The official name is a Great Gross. And while dozen and gross show up in egg cartons, it’s in measurement that the great gross really shines: there are a **dozen **inches in a foot, a **gross **square inches in a square foot, and a **great gross** cubic inches in a cubic foot.

But while the great gross is helping out with set design, there’s a rumor (which we’re apparently happy to help spread) that 1728 actually has a stage name. That’s because there’s a theorem about L-functions of elliptic curves called the Gross-Zagier Theorem, named after Benedict Gross and Don Zagier. So the natural extension of a gross is…a Zagier! Or at least that’s the name that 1728 goes by on the cocktail circuit according to Wikipedia, our local gossip rag. Which makes us wonder where this down-to-earth yet whimsical number will show up next.

*In an amusing turn of events, it turns out that Gross and Zagier won the Frank Nelson Cole prize in Number Theory in 1987 from the American Mathematical Society for their paper “Heegner points and derivatives of L-series” which contained the above theorem. The other winner that year for a different paper was Dorian M. Goldfeld who, the following year, published a paper with M. Anshel entitled “Applications of the Hardy-Ramanujan partition theory to linear diophantine problems,” bringing it all back full-circles to the people who made 1729 famous. It’s like one giant family reunion. *

## Illusion Knitting

April 4, 2011See Mini-G look at this fine piece of stripey art:

Isn’t that interesting, full of nuance? NO — it looks totally boring. But Mini-G is actually looking at it at an angle, which turns out to be a completely different story.

No more simple stripes! And while it’s no Mona Lisa*, it’s pretty cool to see the shapes appear just as you start to walk away in search of something less vertical to look at. Even better, it’s simple knitting. REALLY simple knitting, just knits and purls, where using stockinette stitch makes a color fade into the background when viewed from the side, and using garter stitch makes a color stand out. There’s a great explanation here, where “great”=“uses legos”.

This comes from Woolly Thoughts (“In pursuit of Crafty Mathematics”) and their newish illusion site. It’s a free pattern — Woo hoo! — and not that I’m suggesting that you knit during meetings or anything, but if you DID knit during meetings this particular pattern is simple enough that you can do it without being distracted from the Important Conversations and Presentations, and then you can feel good at the end of two hours that you made quite a bit of progress on your knitting whether the meeting led to a resolution or not, plus you get to point out that you’re really doing mathematics if anyone asks what you’re knitting. Win-win!

* though there is a pattern for that.

## It’s a Threeven Day!

March 3, 2011Happy 3/3 everyone!

I just graded a bunch of proofs that √3 is irrational. The proofs had a lot of holes in them. This didn’t surprise me too much, in large part because the students weren’t math majors; rather, it was for a liberal arts math class taken largely as a gen ed requirement, and the whole proof by contradiction thing is really pretty scary and abstract for most people the first time around under the best of circumstances.

But actually, even when I’ve assigned this to math majors, they struggle. They can have the proof that √2 is irrational right in front of them, be instructed that instead of even numbers they want to look at multiples of 3, and despite my Find and Replace instructions, they still don’t understand what to do. The most common mistake is to replace “even” with “odd”.

In some ways this doesn’t surprise me, but in some ways it does. Why is it such a conceptual leap to go from 2 to 3? It’s a HUGE leap for many people. And so I was pondering this while grading, and Batman suggested it might be because we have a special word for “divisible by 2” but don’t for “divisible by 3”. So you get, what, 10 years of reinforcement that there is just this one special way to divide the integers, and it doesn’t generalize.

What we need is a new word for these numbers.

And fortunately we have one: threeven. So 0, ±3, ±6, ±9, … are all threeven, and the rest are…umm, not. (Maybe we need two new words). This word isn’t mine or even Batman’s; it actually was suggested by one of his students in response to this exact same problem.

As a bonus, it generalizes: there’s fourven, fiven, sixen, seven-en (sev-en? )…as far as you want. Which, admittedly, might not be very far but it still makes for a smoother sounding proof.

Happy threeven day!

## Winter Math Jokes

February 2, 2011It was a crazy January (with an inadvertently extended sabbatical, thanks to the ice storm down south at the time of the Joint Math Meetings!) and now February is coming in like, well, February. Rochester is in the middle of a winter storm, and though it doesn’t quite seem to be the **WINTER STORM **that the forecasters predicted, there’s still a respectable amount of snow and ice. Leading to conversations like these:

**Last night, looking at the closings online:**

**Person 1 : ** Wow, they’ve even closed all the Curves gyms in the area, except for one that’s on a delay. They list them all separately — that’s weird.

**Person 2: **Isn’t that a complicated what of describing it? If they just made one announcement it would be Simple Closed Curves.

*************************

**And then this morning…**

**Person 1: ** Can you take the kids to school tomorrow? I’m giving an exam and want to allow plenty of time to drive slowly if the roads are still icy.

**Person 2: ** Is that a Margin of Terror?

## Mandelbrot Video

January 3, 2011I was thinking of all the things I meant to post in 2010, that I diligently saved, but that became less timely as time went on. D’oh! Crucial mistake, since it turned out the alternative was…blankness.

So I thought it might be fun, at least in a New Year Cleaning sort of way, to post them. And I thought I should call it Ten Things I Meant to Post, But Didn’t Get Around to. Except I’m not sure that there are 10, so this might be a Hitchhiker Trilogy kind of Ten.

Thing #1 was really Saturday’s post: The fact that the subtraction principle in Roman Numerals evolved gradually and (really, like almost everything I think) with some back and forth.

And Thing #2 is this Mandelbrot video, which was passed along by a colleague (Thanks Betsey!) in October, only a few days after Benoit Mandelbrot’s death. So in honor of the man and all that he did, here’s a tribute, prepared several years ago. I hope he saw it and enjoyed it.

From Youtube: *“A music video for Jonathan Coulton’s song Mandelbrot Set by Pisut Wisessing made in Film 324: Cornell Summer Animation Workshop, taught by animator Lynn Tomlinson every summer for Cornell’s summer session, in the department of Theatre, Film & Dance.”*

## Roman Numerals…not quite so simple

January 1, 2011Happy New Year! And since the New Year is all about numbers (especially if you have come to look forward to Denise’s annual January 1 post on Let’s Play Math: form all the integers from 1 to 100 using (exactly) the digits 2, 0, 1, 1 and common mathematical symbols), here’s a picture of a number that I meant to post in ~~October~~ ~~November~~ December.

Recognize this number? Even though it’s not written as LIV? This is from the 54th entryway to the Colosseum in Rome, which was built almost 2000 years ago when Roman numerals didn’t always use the subtraction property that we’re taught, where 4 is written as IV instead of IIII.

I found that to be interesting in and of itself, since I’d heard that the subtraction was a later addition but never witnessed it. But what’s weird? It wasn’t a sudden change. Here’s the forty-fifth gate:

The subtraction principle was used with 40, just not with 4. Which leads to a natural question: what about gate 44?

I’m bummed that we didn’t get a better picture of this, but you can kind of see all four Is after the L. Apparently, according to our usual font of knowledge, the reluctance to use IV is because that was the standard abbreviation for Jupiter’s name in Rome (IVPPTER), and this mixture of sometimes using four symbols in a row continued for more than a thousand years: in the 1390 English cookbook ** The Forme of Cury** (here on Project Gutenberg) the author still uses IIII [as in the Table of Contents, where Section IIII is

*rapes in potage*] and there are also some IV for section numbers and references to Edward, though those might be later additions.

And even 100 years ago [last year, in 1910], the Admiralty Arch in London uses MDCCCCX instead of MCMX in the inscription

ANNO : DECIMO : EDWARDI : SEPTIMI : REGIS :

: VICTORIÆ : REGINÆ : CIVES : GRATISSIMI : MDCCCCX :

(*In the tenth year of King Edward VII, to Queen Victoria, from most grateful citizens, 1910).*

So what does all this mean? Nothing much, except that Roman Numeral Rules were maybe not quite as hard and fast as I once believed.

## Girth Units

December 7, 2010This Brian Regan video isn’t new, but I saw it recently for the first time and found it hilarious (Thanks for the link Michael!). And timely, given the holiday season.

Enjoy!

## Carnival of Mathematics #72

December 3, 2010Welcome to the 72^{nd} Carnival of Mathematics! Have you been waiting all day (sorry!) for it, filled with Anticipation? If so, that would be most appropriate, since according to this site the song *Anticipation *by Carly Simon was the 72^{nd} best song of 1972.

The prime factorization of 72 is 2^{3}·3^{2}, which has a cool kind of symmetry. Inversions also have a cool kind of symmetry, and are explored by **Patrick Vennebush** in Inversions « Math Jokes 4 Mathy Folks posted at Math Jokes 4 Mathy Folks.

In 1889 Nellie Bly went around the world in 72 days (a world record at the time, albeit only for a few months). Thanks to the wonder of the internet, you can read all about it in her book. She seems like a creative kind of gal, and might well have enjoyed the post about enclosures by **Miss Nirvana** in Creating Nirvana: Homeschooling: Box Assemblage posted at Creating Nirvana.

The number 72 is the sum of four consecutive primes (13+17+19+23). It’s also the sum of six consecutive primes (5+7+11+13+17+19). Because the primes are consecutive, the summation is pretty easy to remember. Mnemonics also help make things easy to remember, and in Madhava’s Mnemonic Mathematics, at JOST A MON, **Fëanor** presents a medieval mnemonic for pi from South India.

If you want to know how fast your interest-bearing money is going to grow, you can use the Rule of 72: dividing 72 by the annual interest rate is a pretty good estimate for how long it will take your money to double. For example, at a 6% annual interest rate, your money would double about every 72÷6=12 years. (This is just an estimate, and works pretty well whether the interest is compounded quarterly or daily.) Money is one aspect that people consider when choosing a career. Speaking of careers, **Maureen Fitzsimmons** presents Top 50 Blogs About Careers in Science at Masters in Clinical Research, saying, “When considering a new career, it’s always helpful to learn from people already in the field. These 50 blogs can provide that insight about science careers.”

The human body is made up of 72% water, although since I got that fact from Wikipedia I might have to retract it later. In the post Rates of Scientific Fraud Retractions at Deep Thoughts and Silliness, **Bob O’Hara** explains, “OK, this is stats really – I do a quick analysis of retraction rates to see if Americans really retract more often than anyone else. (Ha!).”

The number 72 is divisible, or nearly so, by all of the integers from 1 to 9. In particular, it has a remainder of Two when divided by 5 or 7, and a remainder of Zero when divided by the other seven numbers, making it a bit of a Zero Hero. For ways that you too can be a Zero Hero, see our next post, Singapore Math: 52 Ways to Become a Zero Hero by **Yan Kow Cheong** at Singapore Math.

World Records allow people from all across the globe to compete for bizarre bragging rights. For example, just this past August, Patrick Lomantini set a World Record by continuously cutting hair for 72 hours in Witchita, Kansas. A simpler way to connect to your worldwide brethren is through podcasts. **Peter Rowlett** demonstrates this effectively in Math/Maths LIVE from MathsJam! at Travels in a Mathematical World, saying, “My American podcast co-host Samuel Hansen visited the UK in November and we did a mathematical tour. As part of this, you can listen to two podcast recordings made live before audiences. This is the first one, from the MathsJam recreational maths weekend.”

Another World Record was set this year by Jeff Miller of Chicago for the longest amount of time continuously watching sports TV: also 72 hours. And another Podcast worth listening to is Math/Maths LIVE from Greenwich!, also posted by **Peter Rowlett**, with the note “This is the second one, from Greenwich.”

John Hart Ely, an oft-cited legal scholar, was born 72 years ago today. It seems likely that he would be fairly well read, and so might have particularly appreciated the post The PiSBN Project by **Geoff Robbins** at Artificial Philosophy, which was “A personal coding project to find ISBN numbers in Pi.”

The number 72 is the smallest number whose 5th power can be written as the sum of five smaller fifth powers:

72^{5}=19^{5} + 43^{5} + 46^{5} + 47^{5} + 67^{5}

If you had to wait for an elevator when there were five unevenly spaced elevators you’d probably be happy if you’d read Where to wait for an elevator — The Endeavour by **John Cook** at The Endeavour.

And finally, the number 72 is 66 in Base 11. That’s nice and straightforward. But **MarcCC **at Good Math, Bad Math likes to look at arguments that are not as straightforward; his post Obfuscatory Vaccination Math (suggested for this Carnival by colleague GrrlScientist) takes a somewhat confusing argument and examines it more closely.

That’s it for this month! Good luck to all the Putnam takers tomorrow, and the next Carnival of Mathematics will occur in January (with a Math Teachers at Play in between!)

## Sierpinski hiding in the Sistine Chapel

December 2, 2010It was the second day in Rome, an intense day of walking and walking and WALKING, made all the harder by the youngest member of our family twisting his foot near the Colosseum. And in a bout of bad timing, this was also the day we had tickets to the Vatican Museum (tickets that cost significantly less than 10 Billion Euros, I’m happy to say), so sore foot or not we forged ahead.

The museums were absolutely amazing, with cool things like actual Babylonian script (no idea what it means because it wasn’t clearly numbers, but still):

Plus, because it was a Friday night and the Museums aren’t always open then (last we heard it was a summer thing, extended through October), there weren’t many people in the main part of the museum. It was dark, and we could look out from nearly empty rooms into nearly empty courtyards:

But the museums are long. Really long. I can’t find the dimensions, but according to my city map they look about 1/3 of a mile, and you basically walk around near the entrance then then down one whole side the entire 1/3ish mile length on the second floor, and then you go return on the bottom floor. By the time we reached the end of the second floor we were already carrying our younger son, and we still had to walk back to get to the exit [and then walk to the Metro, and then the hotel. And it was almost 10pm.] But still, at this halfway point is the Sistine Chapel, and that is not to be missed, no matter how tired.

So we went in the Sistine Chapel, which was the one area that was completely crowded, plus it was really loud in there because the guards kept saying **SHHHHHHHHH** into the microphones and then a recorded voice came on overhead to tell everyone that this was a place of worship and to be quiet, and this was repeated loudly in 8 different languages. So after about 15 seconds of admiring the ceiling we decided to call it a day and begin the trek back. But then, right near the exit, TwoPi suddenly whispered, “It’s a Fractal!” And so I looked at the floor:

See all those Sierpinski Triangles???? They go all the way to Stage 3!

The entire walk back we stopped at every souvenir stand (they’re all over the museum) and had this conversation:

“Do you have any picture of the floor of the Sistine Chapel?”

“You mean the ceiling?”

“No, the floor.”

“No, sorry.”

But then the next day we went to the Mouth of Truth (a giant face where you stick your hand in the mouth, and it gets bit off if you’re a liar), which is part of the church Santa Maria in Cosmedin. The exit from the Mouth of Truth area goes through the church itself, and lo, there were MORE Sierpinski triangles on the floor!

Here:

and here

and smaller ones here:

and curved ones here

There were some other neat shapes, too, like these

and these, which looked just like a quilt

and these

The pieces were all laid out in sections, like…well, I really did think of quilts every time I looked at the floor:

There were even swirly parts that formed a giant infinity.

After taking 800 pictures we finally left, but a few hours later we were at the Basilica of San Clemente, which is a medieval Church built on top of a 4th century church built on top of a Temple of Mithras, and at the most modern level the floor has the same kind of design. We sat and ~~rested our tired feet~~ admired it, but didn’t take any pictures because a Mass was about to start and we didn’t want to intrude.

So what was going on? It turns out that this style of floor is called **cosmatesque**, and Our Friend Wikipedia describes it as:

a style of geometric decorative inlay stonework typical of Medieval Italy, and especially of Rome and its surroundings. It was used most extensively for the decoration of church floors, but was also used to decorate church walls, pulpits, and bishop’s thrones. The name derives from the Cosmati, the leading family workshop of marble craftsmen in Rome who created such geometrical decorations.

So it’s not terribly surprising that we saw three similar floors within 24 hours, even though we’d never seen anything like it before. Sierpinski is hiding out all over the place.

## Clocks Around Rome, Part II

December 1, 2010A few more clocks to show!

Up in the Pincian Gardens, where all the Math Guys are, is a water clock created back in 1867. It only worked for about 40 years, however, and then was in disrepair for about a century. Fortunately, only three years ago the clock was restored and now it totally works. Yay! Here’s what it looked like when we were approaching it:

And here’s what it looked like when we were standing in front of it:

(Many of the clocks in Rome used Roman numerals, heh heh.)

Here’s a close up of the water portion:

The water pours first on one side, then the other.

Finally, here’s a close up of the plaque, which tells a little about it, if you read Italian:

And a 2007 article here by Brian Barrow which tells even more, including:

The timepiece is the result of the work of two men: Father Giovan Battista Embriaco, a Dominican priest and scientist (1829-1903), and the Swiss-Italian architect Gioacchino Ersoch (1815-1902). Apart from teaching physics and mathematics, Embriaco had the hobby of constructing mechanical water clocks (see box) in which the continuous emptying and filling of containers at the ends of a balanced arm produced the rocking motion which took the place of the traditional pendulum by moving a notched wheel at regular intervals.

Despite seeing quite a few neat clocks in Rome, we missed the six-hour clocks. We’d found information about these on a site of Curious and Unusual things in Rome [a fabulous resource!], where it said:

When clocks finally began to appear on important churches and public buildings, some of them had a dial with only six hours, not twelve as in ordinary clocks, so to divide the day into canonical hours, when the prescribed prayers were to be recited. The bells, instead, rung up to twelve times, despite the dial, and the hours were counted up to 24! For instance, at the 21st hour (i.e. around 4 pm in summer) the dial would have shown III, and nine tolls of the bell would have been heard.

Only two of these dials are still extant, in the main cloister of Santo Spirito in Sassia complex, near the Vatican, and on the façade of Santa Maria dell’Orto’s church, in Trastevere district (pictures on the right).

We did sneak over the Santo Spirito, but couldn’t find the clock and there was a wedding just getting out (all the cars had big bows on the antenna; we saw this in another wedding procession the next day) so we didn’t really want to stand and look around. I’m still not sure where it is.

BUT, as a bonus, we did unexpectedly run across two more sundials in the museum in Ephesus.

Ephesus was a Greek city before it became a Roman city before it became a Turkish city, which probably explains the Greek. (Although it’s interesting that it’s letters instead of numbers. Unless the letters are also numbers? And if not, aren’t some letters missing? I’m so confused. Most of the stuff in the courtyard was unlabeled, so I couldn’t find out anything additional.)

Next up, even more math in Rome! *Unless I don’t get to it before Friday’s Carnival of Mathematics, in which case the Carnival will be the next up*.