The Erdös Number Project
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The Erdös Number Project


Read Aug. 1, 2014 News at OU article on the popularity of this website. 



The Erdös Number Project

This is the website for the Erdös Number Project, which studies research collaboration among mathematicians.

The site is maintained by Jerry Grossman at Oakland UniversityPatrick Ion, a retired editor at Mathematical Reviews, and Rodrigo De Castro at the Universidad Nacional de Colombia, Bogota provided assistance in the past.  Please address all comments, additions, and corrections to Jerry at

Erdös numbers
have been a part of the folklore of mathematicians throughout the world for many years.  For an introduction to our project, a description of what Erdös numbers are, what they can be used for, who cares, and so on, choose the “What’s It All About?” link below.  To find out who Paul Erdös is, look at this biography at the MacTutor History of Mathematics Archive, or choose the “Information about Paul Erdös” link below.  Some useful information can also be found in this Wikipedia article, which may or may not be totally accurate.


  • What’s It All About?: General overview, including our (admittedly arbitrary) rules for what counts as a research collaboration.
  • The Data: Lists of all of Paul Erdös’s coauthors and their respective coauthors, organized in various ways.  There are also links to websites of or about Erdös’s coauthors.
  • Facts about Erdös Numbers and Collaborations: Statistical descriptions of Erdös number data, a file of the subgraph induced by Erdös coauthors, Erdös number record holders, facts about collaboration in mathematical research and the collaboration graph, including some information about publishing habits of mathematicians (for example, the median number of papers is 2, and the mean is about 7).  This subpage has loads of information about the collaboration graph and Erdös numbers, including the distribution of Erdös numbers (they range up to 13, but the average is less than 5, and almost everyone with a finite Erdös number has a number less than 8) and “Erdös numbers of the second kind”.
  • Research on Collaboration: Papers on collaboration in scientific research, collaboration graphs and other small world graphs, and Erdös numbers.  A lot of research is currently being done by various scientists on collaboration graphs and related topics.
  • Related Concepts: Six degrees of separation, the Kevin Bacon game, Small Worlds, academic genealogy, Hank Aaron, graph theory.


A nice audio feature about Paul Erdös and Erdös numbers can be found on the Web.

A segment of the NPR program “Ask Me Another” featured a quiz about Erdös numbers.

I recommend a delightful children’s book about Paul Erdös: The Boy Who Loved Math: The Improbable Life of Paul Erdös.

This website was used as the basis for the 2014 Interdisciplinary Contest in Modeling.

There is a project in the works to create a documentary film on Erdös-Bacon numbers.

There is a blog about Erdös numbers on a site discussing mathematicians on Wall Street.

A new paper by Paul Erdös was published in 2015, with coauthors Ron Graham and Steve Butler. This makes Butler the 512th Erdös coauthor. He and his coauthors will be added to the lists at the next update (around 2020).


NOTES: The data shown on this site are based primarily on all items appearing in MathSciNet through mid-2015. 

If you are an Erdös coauthor, I would really appreciate your sending me a complete list of your coauthors (with full names).

One thing we’d really like to do is give more accurate information on some of the old coauthors’ status — whether they are still alive.  Look at the list of coauthors arranged by date of first paper with Erdös; if there is no asterisk after the name, then we assume the person is still alive, except as noted in the addenda file.  If anyone has any information that one or more of these are deceased (or, as Paul Erdös  would say, “have left”), please let me know.  (We know some are alive; please report only those that have passed on, and report only Erdös coauthors, since there is no way we could extend this convention to those with Erdös number 2.)    

I have deleted all links to the unsolicited translations that used to be here, because in some cases people were providing poor translations and linking to commercial sites.
You are visitor number since we started keeping track on July 3, 1996, using web counter.

This page was last updated on April 7, 2017 (but subpages may have been updated more recently).
However, the lists of coauthors and the various other statistics on this site are updated about once every five years.  The current version was posted on July 14, 2015 and includes all information listed in MathSciNet and DBLP through mid-2015.