# Purdue alumnus Yitang Zhang at the International Congress of Mathematicians

**08-21-2014**

The International Congress of Mathematicians (ICM) is the most prestigious venue for mathematicians to present their research. Held once every 4 years, it serves as a time both to report on central advances in mathematics and as a time to celebrate high-profile achievements and awards, including an announcement of the winners of the Fields Medal, commonly called the Nobel Prize of Mathematics.

At the ICM in Seoul, Korea, in August 2014, Purdue Mathematics Alumnus Yitang Zhang (PhD, 1991) delivered the final address of the Congress to report on his ground-breaking work in number theory. His breakthrough concerns what's known as the Twin Prime Conjecture. A Twin Prime is a prime number, *p*, so that *p*+2 is also a prime number. The Twin Prime Conjecture (which has still not been proven) is that there is an infinite sequence of these twin primes.

Zhang's work proves a weaker version of this conjecture. He proved that there is some number, *N*, so that *p* and *p*+*N* are both prime for an infinite sequence of integers, *p*. That is, instead of requiring twin primes, which differ by 2, he allows pairs of primes that differ by some fixed amount and shows that there is an infinite sequence of such pairs. In his original proof, Zhang showed that there is an *N* that is less than 70 million, but further advances show that there is such an *N* that is at most 246. Prior to Zhang's work, it was not known that there was any value of *N* that would produce an infinite sequence of pairs of primes differing by *N*.

Zhang's result stunned many in the mathematical community for the novelty of its proof and for its source. After leaving Purdue, Zhang faced a difficult set of circumstances that led him out of academia for a period of nearly 10 years, during which time he worked a variety of jobs, including in a Subway sandwich shop. In 1999 he was hired as a lecturer at the University of New Hampshire. He continued in that position until January 2014, when he became a full professor at UNH in the wake of his remarkable result. Other honors resulting from Zhang's recent work include the 2013 Ostrowski Prize (awarded in 1989 to Purdue Professor Louis de Branges), the 2014 Cole Prize in Number Theory, and the 2014 Schock Prize in Mathematics.

Former Purdue mathematics professor Minhyong Kim interviewed Yitang Zhang at the Seoul ICM. A transcript of this interview, which includes an inspiring discussion of Zhang's persistence and his love of mathematics, is available here.