## Pi Degrees of Separation

Numbers games and mathematics make a logical combination. So it’s no surprise that the maths world has its own version of the six degrees of separation game. Like the Hollywood game (created around actor Kevin Bacon) this one features a mathematician known for his prolific output: Paul Erdős.

Erdős was a Hungarian mathematician who published more than 1,500 research papers in his lifetime (1913—1996), more than anyone else in his field. He collaborated with other researchers on several hundred of these papers, and it is this high volume of collaborative works that provides the foundation for the six degrees game known as the **Erdős Number**.

A person’s Erdős Number is determined by whether they co-wrote a paper with him, or with someone else who collaborated with him. Paul Erdős has an Erdős Number of 0. His co-authors have an Erdős Number of 1. Anyone who has collaborated with one of his co-authors has an Erdős Number of 2, and so on.

Helpfully, an online calculator has been created to look up someone’s Erdős Number (or their degree of separation away from any other mathematician).

#### Update

Spyros Heniadis has alerted me (in the comments below) to a great Radio Lab podcast which talks about the Erdős Number and Paul Erdős in more detail. It’s worth catching to hear about this extraordinary character, his unconventional life, upbringing and introduction to mathematics. The section on Erdős starts about halfway through the podcast.

*Photo credit: Robbie Sproule*

## 6 Responses to Pi Degrees of Separation

I remember hearing about this on a great Radio Lab episode that you might enjoy.

http://www.radiolab.org/2009/nov/30/

I’ve always enjoyed math even though I didn’t pursue it beyond finite mathematics in college (which sucked btw!), despite that, I have a deep respect and appreciation for numbers and mathematics.

Spyros, I’m really glad you provided the link to the Radio Lab feature. I’ve updated the post to include this. It’s good to hear that your college experience didn’t turn you off mathematics for good.

My boyfriend (who’s a roboticist) told me about this game and it really tickles me– although I’m afraid to look up my Erdos number since me, being a total non-mathematician, can’t really hope to have a good score. Unless, that is, the system gives points to being the girlfriend of a roboticist?

Carolyn: sadly, I don’t think there’s a variant in the online Erdős calculator for girlfriends of roboticists, although you could suggest it as a modification (I’m sure it would provoke a great reaction).

Carolyn, you have to prove something first. Then write a paper on it with someone. And that someone him/herself has to have an Erdos number. Then your Erdos number is that person’s +1.

If you’re not a mathematician, it’s likely you haven’t proven much, and almost certain that you haven’t published any proofs (since the very publishing of a proof yields a Ph.D.).

Regardless, your boyfriend’s status definitely gives you loads of points, so you might claim an Erdos number of i, the imaginary Erdos number!

Bon, I think the notion of an Erdős number of ‘i’ is very fitting (maybe it should also be i for inclusive, as it effectively leaves no one out!).

Apparently the baseball player Hank Aaron is jokingly considered to have an Erdős number of 1, because he and Erdős autographed the same baseball.