Chen's theorem

In number theory, Chen's theorem states that every sufficiently large even number can be written as the sum of either two primes, or a prime and a semiprime (the product of two primes).

The statue of Chen Jingrun at Xiamen University.

It is a weakened form of Goldbach's conjecture, which states that every even number is the sum of two primes.

History

The theorem was first stated by Chinese mathematician Chen Jingrun in 1966,^[1] with further details of the proof in 1973.^[2] His original proof was much simplified by P. M. Ross in 1975.^[3] Chen's theorem is a giant step towards the Goldbach's conjecture, and a remarkable result of the sieve methods.

Chen's theorem represents the strengthening of a previous result due to Alfréd Rényi, who in 1947 had shown there exists a finite K such that any even number can be written as the sum of a prime number and the product of at most K primes.^[4][5]

Variations

Chen's 1973 paper stated two results with nearly identical proofs.^[2]: 158 His Theorem I, on the Goldbach conjecture, was stated above. His Theorem II is a result on the twin prime conjecture. It states that if h is a positive even integer, there are infinitely many primes p such that p + h is either prime or the product of two primes.

Ying Chun Cai proved the following in 2002:^[6]

There exists a natural number N such that every even integer n larger than N is a sum of a prime less than or equal to n^0.95 and a number with at most two prime factors.

Tomohiro Yamada claimed a proof of the following explicit version of Chen's theorem in 2015:^[7]

Every even number greater than ${\displaystyle e^{e^{36}}\approx 1.7\cdot 10^{1872344071119343}}$ can be represented as the sum of a prime and a product of at most two primes.

In 2022, Matteo Bordignon found multiple errors in Yamada's proof, and provided an alternative proof for a lower bound:^[8]

Every even number greater than ${\displaystyle e^{e^{32.7}}\approx 1.4\cdot 10^{69057979807814}}$ can be represented as the sum of a prime and a square-free number with at most two prime factors.

Also in 2022, Bordignon and Valeriia Starichkova ^[9] showed that the bound can be lowered to ${\displaystyle e^{e^{15.85}}\approx 3.6\cdot 10^{3321634}}$ assuming the Generalized Riemann hypothesis (GRH) for Dirichlet L-functions. In 2024, Bordignon and Starichkova ^[10] improved this result by lowering the bound to ${\displaystyle e^{e^{14}}\approx 2.5\cdot 10^{522284}}$.

References

Citations

1. Chen, J.R. (1966). "On the representation of a large even integer as the sum of a prime and the product of at most two primes". Kexue Tongbao. 11 (9): 385–386.
2. Chen, J.R. (1973). "On the representation of a larger even integer as the sum of a prime and the product of at most two primes". Sci. Sinica. 16: 157–176.
3. Ross, P.M. (1975). "On Chen's theorem that each large even number has the form (p₁+p₂) or (p₁+p₂p₃)". J. London Math. Soc. Series 2. 10, 4 (4): 500–506. doi:10.1112/jlms/s2-10.4.500.
4. University of St Andrews - Alfréd Rényi
5. Rényi, A. A. (1948). "On the representation of an even number as the sum of a prime and an almost prime". Izvestiya Akademii Nauk SSSR Seriya Matematicheskaya (in Russian). 12: 57–78.
6. Cai, Y.C. (2002). "Chen's Theorem with Small Primes". Acta Mathematica Sinica. 18 (3): 597–604. doi:10.1007/s101140200168. S2CID 121177443.
7. Yamada, Tomohiro (2015-11-11). "Explicit Chen's theorem". arXiv:1511.03409 [math.NT].
8. Bordignon, Matteo (2022-02-08). "An Explicit Version of Chen's Theorem". Bulletin of the Australian Mathematical Society. 105 (2). Cambridge University Press (CUP): 344–346. arXiv:2207.09452. doi:10.1017/s0004972721001301. ISSN 0004-9727.
9. Bordignon, Matteo; Starichkova, Valeriia (2022). "An explicit version of Chen's theorem assuming the Generalized Riemann Hypothesis". arXiv:2211.08844.
10. Bordignon, Matteo; Starichkova, Valeriia (2024). "An explicit version of Chen's theorem assuming the Generalized Riemann Hypothesis". The Ramanujan Journal. 64: 1213–1242. doi:10.1007/s11139-024-00866-x.

Books

• Nathanson, Melvyn B. (1996). Additive Number Theory: the Classical Bases. Graduate Texts in Mathematics. Vol. 164. Springer-Verlag. ISBN 0-387-94656-X. Chapter 10.
• Wang, Yuan (1984). Goldbach conjecture. World Scientific. ISBN 9971-966-09-3.

External links

• Jean-Claude Evard, Almost twin primes and Chen's theorem
• Weisstein, Eric W. "Chen's Theorem". MathWorld.