The Erdös number honors the late Hungarian mathematician Paul Erdös, one of the most prolific writers of mathematical papers. It is a way of describing the "collaborative distance", in regard to mathematical papers, between an author and Erdös.
"And What Is Your Erdös Number?", Casper Goffman, American Mathematical Monthly, Vol. 76, No. 7 (August-September 1969), p. 791.
My Erdös number is 5, since I coauthored a paper with Bart Childs, and his Erdös number is 4, etc., down to Paul Erdös himself, who has an Erdös number of zero. Actually, I should say that my Erdös number is no more than 5, since there may be a shorter path that I haven't found yet.
McGuire ---> Childs ---> Osborne ---> Turlach ---> Vijayan ---> Erdös
Childs, S. Bart; Osborne, Michael R. Fitting solutions of ordinary differential equations to observed data. Computational techniques and applications: CTAC95 (Melbourne, 1995), 193--198, World Sci. Publ., River Edge, NJ, 1996.
Czarn, Andrew; MacNish, Cara; Vijayan, Kaipillil; Turlach, Berwin Statistical exploratory analysis of genetic algorithms: the influence of Gray codes upon the difficulty of a problem. AI 2004: Advances in artificial intelligence, 1246--1252, Lecture Notes in Comput. Sci., 3339, Springer, Berlin, 2004.