While the claim has yet to be independently verified, Yu has been heralded as the real-life Will Hunting. Just don’t ask him about the film — he says he’s never seen it. Nor is the comparison between Damon’s character and Yu perfectly apples-to-apples: Where Hunting was a south Boston roughneck, Yu is reportedly shy and self-effacing, calling himself “slow-witted” in interviews.
Training at a vocational school before joining the logistics company, Yu has not spent much time in ivory towers. He was a migrant worker, delivering items and stopping at the local university to learn about math when he could.
“He has never received any systematic training in number theory nor taken advanced math classes,” Zhejiang University mathematics professor Cai Tianxin told CNN. “All he has is an instinct and an extreme sensitivity to numbers.”
To the website Chinatopix, Cai described Yu’s method as “a very imaginative solution.”
Yu’s work involves Carmichael numbers, a set of odd numbers also known as “pseudoprimes.” There are certain mathematical tests, like Fermat’s little theorem, that show if a number is prime. Pseudoprimes, like Carmichael numbers, may at first blush appear to pass some of these tests. But repeated examinations show that Carmichael numbers are not actually prime (the numbers are divisible by other factors than 1 or themselves).
There are technically an infinite amount of Carmichael numbers, though they occur very infrequently. In 1910, R. D. Carmichael found just 15 of these pseudoprimes, the first five of which are 561, 1105, 1729, 2465 and 2821. Figuring out which numbers are prime and which are Carmichael numbers can be tricky work. In the search for increasingly large prime numbers, it is important to identify which ones are the so-called liar numbers. If this seems like a lot of computational effort to find something you might have learned about in fourth grade, consider that prime numbers are more than a mathematical curiosity — they power encryption systems like the RSA algorithm used in online shopping.
“I made my discoveries through intuition,” Yu said to China Daily, a state-backed Chinese newspaper. “I would write down what I thought when inspiration struck about the Carmichael.”
Pending independent verification of his technique, Yu may have found a way to more easily weed out the Carmichael numbers from the true primes. According to China Daily, Yu worked on his proof for eight years. He reached out to several professors, but Cai was the first to respond to a letter from Yu.
In June, Cai invited Yu to give a demonstration of his proof at Zhejiang University. As he spoke, Yu reportedly did not use a guide or reference sheet, relying solely on memory during the lecture. Experts in attendance were split, the Daily reported, regarding Yu’s work either as “novelty” or his results having “a certain depth.”
William Banks, an expert on Carmichael numbers at the University of Missouri, told CNN there had not been a such development in this field for two decades.
“There have been additional theoretical results in this area — including several by myself and my co-authors — but these are all variations on a theme,” he said. Should Yu’s work prove to be true, it would be a significant alternative to what already exists.
Prime numbers have a bit of cachet in mathematical circles. “It’s sort of like finding a diamond,” Chris Caldwell, a professor at the University of Tennessee at Martin who keeps a record of giant primes, told New Scientist in 2013. “People like these large primes and so they also have a value.” The liar counterparts aren’t quite as valued, but anything that can lessen computationally intensive searches is a boon.
Cai plans to publish Yu’s theory in a book on Carmichael numbers. Yu has become something of a local hero, receiving a job offer to work in mathematics rather than package delivery.
For Yu, there is one part of “Good Will Hunting” left to emulate — the love interest. Yu, who is single, told CNN his current aspiration is to start a family.
“I want to have my own family first,” he said, “and then comes math.”