Have you ever wondered about the mathematics behind the idea of "six degrees of separation?" The Erd's Number Project offers several fairly comprehensive lists of co-author relationships to elaborate (with a bit of humor) studies of the dynamics involved in "the collaboration graph," which the website says is "a 'real-life' fairly large graph for combinatorialists to study." The co-author...

The brainchild of retired mathematics professor Harry B. Coonce, this site has the modest goal of listing information about everyone who has earned a doctorate in mathematics during the 20th century. This will allow mathematicians to trace their academic "family tree" and discover their advisor's advisor, their advisor's "siblings" at graduate school, and so on. With over 28,000 names from 380...