Goldbach conjecture can be roughly divided into two kinds (the former is called "strong" or "double Goldbach conjecture" and the latter is called "weak" or "triple Goldbach conjecture"): 1. Every even number not less than 6 can be expressed as the sum of two odd prime numbers; 2. Every odd number not less than 9 can be expressed as the sum of three odd prime numbers. Consider expressing even numbers as the sum of two numbers, each of which 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". In 1966, Chen Jingrun proved "1+2", that is, "any big even number can be expressed as the sum of a prime number and another number whose prime factor is not greater than 2". It is only one step away from guessing "1+ 1" right away.