1 Me: Hmmm. Having appeared in a comic with Kevin Bacon, I just need to get my other good friend Paul Erdős in a strip to attain an Erdős-Bacon number of 2!
2 Me: The only difficulty is that that would require me to think up a joke involving combinatoric theory.
3 {beat}
4 Me: Well, I'm sure I can arrange something.
4 [small caption]: This comic co-authored by David Morgan-Mar and Paul Erdős

Paul Erdős was a Hungarian mathematician who worked on various fields of mathematics, and was incredibly prolific in his publications. He was so prolific, that friends of his invented a joke concept known as the Erdős number.

A person's Erdős number is defined as:

• 0 if you are Paul Erdős.
• 1 if you co-authored a research paper with Erdős.
• 2 if you co-authored a paper with someone with Erdős number 1.
• And so on.

This concept has been around for decades, and is well-known within the mathematics research community. It is the origin of the relatively recent Bacon number discussed in recent strips in this very webcomic, which measures a similar form of separation from Kevin Bacon, with the connections being acting appearances in the same film.

This led to the natural extension of the Erdős-Bacon number, being the sum of one's Erdős and Bacon numbers. Since the requirement involves both having a published research paper and having acted in a film, the number of people with well-defined Erdős-Bacon numbers is quite low. Without stretching the strict definitions, the lowest Erdős-Bacon number known is 3, belonging to mathematician Daniel Kleitman, who wrote a paper with Erdős and appeared as an extra in Good Will Hunting, starring Minnie Driver, who appeared in Sleepers with Kevin Bacon.

My favourite, though, is that Natalie Portman has a strictly defined Erdős-Bacon number, which is 6, thanks to her co-authorship on a paper entitled "Frontal Lobe Activation during Object Permanence: Data from Near-Infrared Spectroscopy", published in the journal NeuroImage. Beautiful and smart.

Although, strictly speaking, I don't have a finite Bacon number, I have written published research papers (in astronomy), and one was co-authored with a computer scientist/mathematician. My Erdős number, to the best of my knowledge, is 4:

David Morgan-Mar and Geoff Bailey, "Xvoigt - An interactive absorption line fitting program for the X Window System," Publications of the Astronomical Society of Australia 12 (2), 1995.

Geoff Bailey and Elias Dahlhaus, "Recognition of path graphs in linear time," Theoretical Computer Science (Ravello, 1995), 201-210, World Sci. Publ., River Edge, NJ, 1996.

Elias Dahlhaus and Wayne D. Goddard, "MAD trees and distance-hereditary graphs," Discrete Applied Mathematics 131 (2003), no. 1, 151-167.

Wayne D. Goddard and Paul Erdős, "Crossing families," Combinatorica 14 (1994), no. 2, 127-134.

Oh, and by the way, Paul Erdős' major field of research was combinatoric theory, a major part of which deals with permuting, or arranging, things.

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2016-10-22 Rerun commentary: The worst thing about writing about Paul Erdős is that his name uses a Hungarian double acute accent, which is different from an umlaut and doesn't have an easy-to-remember HTML entity code, so every time I type it in I have to look it up or copy it from existing text.

I'd like to see a band adopt a name that instead of using a gratuitous heavy metal umlaut instead uses a heavy metal double acute accent. Something like: Gőatcrűsher.