The landlord's name is wrong by a word.

① One of the famous problems in number theory. 1742, the German mathematician Goldbach proposed that every even number not less than 6 is the sum of two odd prime numbers; Every odd number not less than 9 is the sum of three odd prime numbers. In fact, the latter is the inference of the former. For more than 200 years, many mathematicians have been fighting for it, but they have never fully proved it. 1966, Chinese mathematician Chen Jingrun proved that "any sufficiently large even number can be expressed as the sum of numbers whose factor of a prime number and another prime number is not more than 2", which is referred to as "1 2" for short. This is by far the best achievement in the study of Goldbach conjecture in the world. ② Reportage. Author: Xu Chi. Published in 1978. Mathematician Chen Jingrun loved mathematics since childhood. After entering the Department of Mathematics of Xiamen University, he became attached to Goldbach's conjecture, a world-famous mathematical problem. Although he was criticized and treated unfairly during the Cultural Revolution, he still immersed himself in mathematics and finally completed the internationally recognized "Chen Theorem". His works are gorgeous and full of philosophy.

Can all even numbers greater than 2 be expressed as the sum of two prime numbers?

This question was put forward by the German mathematician C Goldbach (1690- 1764) in a letter to the great mathematician Euler on June 7th, 742, so it is called Goldbach conjecture. On June 30th of the same year, Euler replied that this conjecture may be true, but he could not prove it. Now, the general formulation of Goldbach conjecture is: every even number greater than or equal to 6 can be expressed as the sum of two odd prime numbers; Every odd number greater than or equal to 9 can be expressed as the sum of three odd prime numbers. In fact, the latter proposition is the inference of the previous one.

Goldbach conjecture seems simple, but it is not easy to prove, which has become a famous problem in mathematics. In 18 and 19 centuries, all number theory experts did not make substantial progress in proving this conjecture until the 20th century. 1937 Soviet mathematician vinogradov (ииногралов, 189 1- 1983).

It is directly proved that Goldbach's conjecture is not valid, and people adopt "circuitous tactics", that is, first consider expressing even numbers as the sum of two numbers, and each number is the product of several prime numbers. If the proposition "every big even number can be expressed as the sum of a number with no more than one prime factor and a number with no more than b prime factors" is recorded as "a+b", then the Coriolis conjecture is to prove that "1+ 1" holds. Since the 1920s, some mathematicians from abroad and China have successively proved the propositions of "9+9", "23", "1+5" and "L+4".

1966, Chen Jingrun, a young mathematician in China, successfully proved "1+2" after years of painstaking research, that is, "any big even number can be expressed as the sum of a prime number and another number whose prime factor does not exceed 2". This is the best achievement in this research field so far, and it is only one step away from taking off the jewel in the crown of mathematics that caused a sensation in the mathematics field. But this small step is hard to take. "1+2" is called Chen Theorem.

Goldbach's problem can be inferred from the following two propositions. As long as the following two propositions are proved, the conjecture is proved:

(a) Any > even number =6 can be expressed as the sum of two odd prime numbers.

(b) Any odd number > 9 can be expressed as the sum of three odd prime numbers.

This famous mathematical problem has attracted the attention of thousands of mathematicians all over the world. 200 years have passed and no one has proved it. It was not until the 1920s that people began to approach it. 1920, the Norwegian mathematician Bujue proved by an ancient screening method that every even number greater than 6 can be expressed as (9+9). This method of narrowing the encirclement is very effective, so scientists gradually reduce the number of prime factors of each number from (99) until each number is a prime number, thus proving Goldbach's conjecture.

At present, the best result is proved by Chinese mathematician Chen Jingrun in 1966, which is called Chen Theorem. "Any large enough even number is the sum of a prime number and a natural number, and the latter is just the product of two prime numbers." This result is often called a big even number and can be expressed as "1+2".

Before Chen Jingrun, the progress of even numbers can be expressed as the sum of the products of S prime numbers and T prime numbers (referred to as the "s+t" problem) as follows:

1920, Bren of Norway proved "9+9".

1924, Rademacher proved "7+7".

1932, Esterman of England proved "6+6".

1937, Ricei of Italy proved "5+7", "4+9", "3+ 15" and "2+366" successively.

1938, Byxwrao of the Soviet Union proved "5+5".

1940, Byxwrao of the Soviet Union proved "4+4".

1948, Hungary's benevolence and righteousness proved "1+c", where c is the number of nature.

1956, Wang Yuan of China proved "3+4".

1957, China and Wang Yuan successively proved "3+3" and "2+3".

1962, Pan Chengdong of China and Barba of the Soviet Union proved "1+5", and Wang Yuan of China proved "1+4".

1965, Byxwrao and vinogradov Jr of the Soviet Union and Bombieri of Italy proved "1+3".

1966, China Chen Jingrun proved "1+2".

The most difficult problem in Goldbach's conjecture, 1+ 1, has yet to be solved.