"Groups, Graphs, and Erdös Numbers," by Ivars Peterson. Science News Online, June 12, 2004.
Peterson dispels the idea that mathematicians work in solitary pursuit, by using Erdös as an example of one who collaborated extensively with others---as evidenced by what mathematicians refer to as the "Erdös Number." The Erdös number describes the relationship between Erdös and authors who worked with him or one of his associates. Erdös is assigned the number 0; as of the end of 2003, 509 mathematicians had written a paper with Erdös and are forever assigned number 1; 6,984 wrote a paper not with Erdös but with one of his coauthors, so they have an Erdös number of 2---and so on. Peterson notes that Jerrold Grossman (Oakland University, Rochester, MI) worked with Patrick Ion (at Mathematical Reviews ®) and Rodrigo De Castro (Universidad Nacional de Columbia, Bogota) to put together a complete list of Erdös number 1's and 2's. The article notes that many mathematicians enjoy the challenge of determining such networks, and references two websites that show the connectedness of non-mathematicians: the Oracle of Bacon and the Oracle of Baseball.
--- Annette Emerson