5 can be decomposed into 1 and 4,2 and 3,4 and 1, 3 and 2, 1 and 4,5,2 and 3 can be synthesized. But there cannot be 0. Mathematically, integer decomposition is also called prime factorization, which is to write a positive integer as the product of several divisors.

For example, the number 45 can be decomposed into 9*5. According to fundamental theorem of arithmetic, this decomposition result should be unique. In multiplication, 0 multiplied by any number equals 0, so there can be no 0 in integer decomposition.

Decomposition and composition formula:

2 can be divided into 1 and 1.

3 can be divided into 1 and 2,2 and 1.

4 can be divided into 1 and 3,2 and 2,3 and 1

5 can be divided into 1 and 4, 2 and 3, 3 and 2, 4 and 1.

The formula of number decomposition and composition: children should remember "9 to 1", "8 to 2", "7 to 3", "6 to 4" and "5 to 5".

The method of filling ten is simple and easy, and the thinking process includes "looking at a large number, dividing it by two, filling ten by three and adding four".

Look at large numbers, divide them into decimals, make up ten, and add up the remainder.