* Photo: Sian Kennedy * In the new *Futurama* DVD *Bender's Big Score*, the characters encounter Al Gore driving a taxi — a hybrid taxi, naturally. Some viewers may chuckle when they notice that the license plate on the former Vice President's cab reads NOCO2. But very few will realize that the the badge number on another cab, 87539319, is also a joke.

Math geeks, however, will find that number hilarious because of something that happened about a century ago. The British mathematician G.H. Hardy was paying a call on the Indian mathematician Srinivisa Ramanujan. "I had ridden in taxi cab number 1729 and remarked that the number seemed to me rather a dull one," Hardy later recalled. Ramanujan disagreed. "It is a very interesting number," he insisted. "It is the smallest number expressible as the sum of two cubes in two different ways."

The number 1729 can be expressed as 1^{3} + 12^{3} or it can be expressed as 9^{3} + 10^{3}. The number 87539319 can be expressed as the sum of two cubes in three different ways, as 167^{3} + 436^{3} or as 228^{3} + 423^{3}, or 255^{3} + 414^{3}. Much scholarly research has since been dedicated to so-called taxicab numbers like these. Which means that a tiny percentage of mathematically inclined *Futurama* viewers will get a chuckle when they see a cartoon taxi that has a taxicab number printed on it.

*Futurama*, a show made by geeks for geeks, is shot through with impossibly obscure references like that. "The number on Al Gore's cab in that scene also has a secret meaning," says David X. Cohen, who codeveloped *Futurama* with Matt Groening and serves as showrunner. Cohen refuses to reveal the other gag, but if you visit a fan site like GotFuturama.com a few days after the DVD goes on sale, you're likely to find a screenshot and a detailed explanation written by one of the hardcore fans. "If you care enough, you frame-advance through it," says Cohen. "They've earned that moment of pleasure."

Cohen takes his math very seriously. In his office at Matt Groening's studio, he shows me a 25-year-old plaque commemorating a math team victory. He placed third in the entire state of New Jersey, and his team from Dwight Morrow High School in Englewood took first place in the state during his senior year, irking the preppies they competed against. "It killed them that they were beaten by public school kids," he chuckles.

"As a general rule, I hate watching TV or movies with mathematicians in it," Cohen says. "It never rings true. They're portrayed as magic beings. There's an implication that a normal person can't do math because they don't have this magic power, which is very discouraging. You don't have to have Math-Ray Vision." Cohen is wearing a Math-Club T-shirt. Unlike the plaque, this shirt isn't a cherished memento from his childhood. It's from an actual club for grownup math fans in the LA area.