In mathematics, Goldbach conjecture is called the jewel in the crown of mathematics. German mathematician Goldbach put forward the proposition that any odd number greater than 7 is the sum of three prime numbers. This proposition has not been proved. Later, the mathematician Euler put forward another proposition: any even number greater than 6 is the sum of two prime numbers, but he failed to prove this proposition. The above two propositions are collectively called Goldbach conjecture. Since Goldbach put forward this conjecture, many mathematicians have been trying to conquer it, but they have failed. 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 usually called (1+2).