## Mark Washburn

### It figures: We mark the plucky number pi

Until social media, the holiday scheduled for Monday was an exclusive affair, like one of those dreary Druid gatherings where you needed to know somebody in the troop to get in.

Now Pi Day is a fixture in the public domain, celebrated by school kids and mystic numerologists.

Mathematicians used to be the only ones interested. They’d assemble and engage in the spectrum of hilarity only they could appreciate.

They’d tell pi jokes. What snake has a circumference of 3.14? A pi-thon! Statistics show 3.14 percent of sailors are pi-rates! On and on, without end.

Like Kardashian rumps, pi has inexplicably gained a populist following. Monday is 3-14-16, a close approximation to the number that expresses the ratio of a circle’s circumference to its diameter, or 3.14159 for short. It’s a number whose end has never been found.

It’s an irrational number, which means it cannot be expressed as a proper fraction.

Rational numbers get up in the morning, wash their hair and apply tasteful makeup, then go out and perform their calculations with the grandeur of Romanian acrobats.

Irrational numbers stand on the corner in wool caps, smoking cigarettes and looking for work. They don’t get the same respect.

Every spring, Tim Chartier is Charlotte’s most famous mathematician. For the last few years, he and his students at Davidson College have been refining calculations to predict NCAA basketball tourney winners.

They’ve been getting remarkable results. This year they’re noodling a formula to predict Cinderella teams.

Chartier is an applied mathematician, meaning he enjoys math theory, but he’s in the business for results.

On the opposite side of the whole pi enterprise are numerologists, who delight in the enigmatic mysteries found in enumeration.

“Numeracy stuff isn’t prevalent among mathematicians,” says Chartier in a tone that indicates there is a bit of a strain between the disciplines.

Still, pi attracts wonder when you get to know it. Get into it to a couple billion decimal points and you’ll likely find your phone number smiling up at you.

Mystic scenery along the road of pi includes the so-called Feynman point, a sequence of six consecutive 9s beginning at the 762nd position. It’s like driving across boring Kansas and suddenly running into a mastodon.

If you keep driving to 193,034 decimal points, you hit another island of six 9s. Get to position 590,331,982 and you’re rewarded with a thicket of nine 9s, which repeat at position 640,787,382. What does it mean?

Who knows? That’s the fun.

So enjoy Monday, whatever your pi fancy may be. Just stay away from those giddy mathematicians, celebrating the only number that is plainly irrational, but absurdly round.