This is Goldbach's conjecture, commonly known as 1+ 1, which no one can prove at present. At present, the most advanced is 1+2 proved by China mathematician Chen Jingrun, that is, any big even number can be expressed as the sum of a prime number and another prime number factor not exceeding 2. However, although Chen Jingrun proved 1+2, it is said that only another mathematician in the world can understand his proof except himself.