# Carnival of Mathematics 69

# carnival of mathematics 69 – September 3, 2010

Normally a Carnival of Mathematics opens with a discourse on its ordinal. But 69?

It is 1000101 in binary, 1011 base 4, 105 base 8, 45 in hex…If we used 32 as a base? 25. And that would be 15 in base 64.

69 is odd. But there are as many odd numbers as there are ________. I still love that! It is one of a bunch of surprises that **Dave Richeson** lists at Division by Zero. (Mathematical surprises is the post)

69 is semiprime, but there are lots of those. (the product of two primes). And since both primes are congruent to 3 mod 4, 69 is a Blum integer.

69 is 3 times 23, and there were 23 submissions to this carnival (not counting spam). What’s the chance of that happening?

69! is the largest factorial not to cause overflow on most scientific calculators. ( ) Which brings up early, and slightly out of place, **John Cook’s** How to compute log factorial — The Endeavour posted at The Endeavour. Which naturally leads to **Gaurav Kumar****‘s** Last Non-zero Digit of Factorial posted at COME ON CODE ON.

And finally (you were waiting for this?), 69 looks just like 69 when it is rotated 180°. Leading to a much “earthier” transferred meaning, which we won’t delve into here. With just one exception: this “not safe for work” xkcd extension. (click at your own risk.) And for those of you who clicked even though you didn’t want to, any further discussion of sex in this carnival will be cartoon-free. Promise.

For my convenience (and I hope, yours) the 69th carnival is presented in a few chunks:

- popular
- investigations/computation
- probability/stats/data
- P vs NP (math headline of the year)
- history/biography

**Popular**

**Colin Beveridge** continues our “earthiness” with The Dating ‘Rule’ posted at The Joy of Sec(x). Colin is concerned with the question of when you are too young to date. If you like that topic, you might also want to see this post by Tanya Khovanova about externally imposed social differences between male and female mathematicians and this post about the unfairness of the sexual division of labor. And returning to the half+7 rule, this cartoon from…. wait for it…. xkcd. (this is safe, boys and girls)

**Peter Rowlett** presents Prime birthdays via Wolfram|Alpha posted at Travels in a Mathematical World, saying “some friends on Twitter were discussing ‘prime birthdays’, which are days when the number of days since you were born is prime. Here I use Wolfram|Alpha to find your upcoming prime birthdays.”

**Caroline Mukisa** provokes with Finger counting: The Debate Continues! at Maths Insider.

**Yan Kow Cheong** presents The Abacus as a Divination Tool posted at Singapore Math.

And** ****Patrick Vennebush** posted What’s in a Name? « Math Jokes 4 Mathy Folks at Math Jokes 4 Mathy Folks. It’s a game. Or a puzzle. Super-cool, recreational. Go, play.

**Investigations/Computation**

**Carol Cronin** presents Nine Cool Points on the Complex Plane posted at Wolfram Blog.

**Vicky Neale ** writes about theorems. Here she discusses Theorem 33: the size of Gauss sums posted at Theorem of the week. Robin Whitty (who does the same thing, but 7 times as often) submitted the post, saying, “No connection to my website – this is a lovely blog by Vicky Neale whom I don’t know but is a student of Ben Green at Cambridge”

**Alasdair McAndrew** presents The NSH method for matrix inversion posted at Alasdair’s musings. And, drumroll please, he cites a professor (computational theorist, I believe) who I have met IRL. Who actually observed me teaching.

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**Matthew Kähle** writes God’s number is 20 at mathematical musings. “Every Rubik’s Cube, no matter how mixed up, can be solved in 20 moves or less.” Submitted by Fëanor.

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**Ben Blum-Smith** (no relation, to my knowledge, to the Blum Integers, see above) presents Partial Illumination for the Chords-of-an-Ellipse Problem posted at Research in Practice, saying, “Investigation into the ellipse extension of Sam Shah’s points-on-a-circle problem“

**Probability/Stats/Data**

**Bob O’Hara** posted The Palin Effect at This Scientific Life, analyzing “the statistics behind Palin’s effect on the 2008 election.”

And another Bob O’Hara, this time posted at Deep Thoughts and Silliness, about Semiotics and Statistics. Submitted by GrrlScientist.

**P. Surya Prakash** presents Concept of Geometric Probability posted at Clear Your Doubts in Maths and Statistics.

**Glowing Face Man** presents The Hope Function posted at Xamuel.com, saying, “Suppose a desk with eight drawers has an 80% chance of containing a letter. As you search drawers fruitlessly one by one, how does that 80% probability change in time? What about the probability the letter will be in the very next drawer?”

**Simon Rogers** presents Florence Nightingale, datajournalist: information has always been beautiful | News | guardian.co.uk posted at Guardian, saying, “On Florence Nightingale’s innovations in the visualisation of statistics.” Excellent graphic representation of data. Submitted by Fëanor.

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**P vs NP**

**Mike Croucher** presents Proofs, Proofs, Who Needs Proofs? posted at Gödel’s Lost Letter and P=NP, saying, “I like this one. Good fit for the carnival do you think?” Mike is always the Carnival King. He’s who you contact if you want to host.

**Brent Yorgey** presents P vs NP: What’s the problem? posted at The Math Less Traveled, saying, “See also http://www.mathlesstraveled.com/?p=744 for more context.”

And **Mark CC** at Goodmath/Badmath (note the new URL) weighs in with Holy freaking cow! P != NP??. (submitted by GrrlScientist who turns out to be a superhero ornithologist with a secret identity. Go Birds!)

**History/Biography**

We have two tidbits, one old, one new

**Denise** presents Math History Tidbits: The Battling Bernoullis posted at Let’s Play Math!, saying, “Find out why William Dunham called the Bernoulli brothers “the kind of people who give arrogance a bad name.””

**Fëanor** presents a translation from the Russian of a three-part interview with two Field Medalists of 2002: Vladimir Voevodsky and Laurent Lafforgue: Olga Orlova and the Fields Medallists – Part I posted at JOST A MON.

**End**

That concludes this edition. Submit your blog article to the next edition of **carnival of mathematics** using our carnival submission form. Past posts and future hosts can be found on our blog carnival index page.

The next edition of **Math Teachers at Play** (MTaP) will be hosted right here, in two weeks. (See the current edition at The Number Warrior). You may submit directly to me, or through the handy carnival tool.

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Awesome carnival Jonathan, thanks for hosting.

My goodness, I forgot to submit.