“ An individual’s Erdős–Bacon number is the sum of one’s Erdős number—which measures the ‘collaborative distance’ in authoring mathematical papers between that individual and Hungarian mathematician Paul Erdős—and one’s Bacon number—which represents the number of links, through roles in films, by which the individual is separated from actor Kevin Bacon. These numbers, the primary measures of the small world phenomenon in academia and entertainment, respectively, are generally allowed to be more flexible for Erdős–Bacon number calculation, as few published academics have also been professional actors.
http://en.wikipedia.org/wiki/Erdos-Bacon_number
