"1+S" and Chen Theorem
It was not until the 1920s that people began to approach it. 1920, the Norwegian mathematician Brown proved by an ancient screening method, and reached a conclusion that every even number with a large ratio can be expressed as (9+9). This method of narrowing the encirclement is very effective, so scientists gradually reduce the prime factor in each number from (99) until each number is a prime number, thus proving Goldbach's conjecture. At present, the best result is proved by China 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, while the latter is only 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 "s+t" problem) as follows: 1920, Norwegian Brown proved "9+9". 1924, Latmach of Germany proved "7+7". 1932, Esterman of England proved "6+6". 1937, Lacey in Italy successively proved "5+7", "4+9", "3+ 15" and "2+366". 1938, Bukit Tiber of the Soviet Union proved "5+5". 1940, Bukit Tiber of the Soviet Union proved "4+4". 1948, Rini of the Hungarian Empire proved "1+C", where c is an infinite integer. 1956, Wang Yuan of China proved "3+4". 1957, Wang Yuan of China 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, Buchwitz Taber and vinogradov Jr. of the Soviet Union and Pemberley of Italy proved "1+3". 1966, China Chen Jingrun proved "1+2". It took 46 years from Brown's proof of 1920 of "9+9" to Chen Jingrun's capture of 1966 of "+2". Since the birth of Chen Theorem for 30 years, it is futile for people to further study Goldbach conjecture.