Yu Jianchun has never seen Good Will Hunting, and maybe he doesn't need to. CNN reports the 33-year-old Chinese migrant worker is living part of its plot. Yu attended a vocational school rather than college, and he's never taken advanced math—"I barely have any knowledge about calculus or geometry," he says—and yet mathematicians say the employee of a package delivery company has come up with a "more efficient" way to identify Carmichael numbers, or pseudoprimes. The Washington Post explains that these "odd" and "infrequent" numbers can pass some of the tests used to determine if a number is prime (that is, only divisible by 1 or itself). But they aren't: Carmichael numbers have at least three positive prime factors; 561, the first and smallest of 15 such numbers found by RD Carmichael in 1910, is the product of 3 x 11 x 17.
China Daily reports Yu spent eight years working on Carmichael formulas and tried to contact math professors via email and in-person visits to universities. Professor Cai Tianxin of Zhejiang University was impressed by the work, replied, and invited Yu to present his proof at a June 13 lecture. Yu describes himself as so nervous he "wrote wrong numbers on the blackboard." Cai now plans to include Yu's "very imaginative solution" in his latest book, and that's not all Cai is doing for Yu: He told the man's story to Ling Lanfang, president of Silk Road Holding Group. Impressed, Ling has offered Yu what China Daily reports is a "statistics-related position" that Ling says would "give him better development for a career and also more time for furthering his interest and talent in mathematics." (Another study found that genuine prime numbers just got a little stranger.)