Some are just marks, which have been used all the time, such as the symbol of pi, and accumulation is just a mark. There is no special meaning:

Natural number set: n

Integer set: z

Rational number set: q

Real number set: r

Complex set: c

In fact, there is a reason why irrational number sets are not represented by letters. To understand this truth, we must first understand three basic concepts: set, binary operation and closure.

Concepts in mathematics

We are very clear about the concept of set, which refers to a group of elements with certain properties. Of course, there are still many places to discuss about the precise definition of set, but understanding at this level is enough.

Binary operations have not been precisely defined before. Described in less formal language, binary operation is the corresponding law of turning two numbers into one. For example, addition is a binary operation because it changes 1 and 1 into 2, 2 and 3 into 5 and so on. Similarly, the four operations of addition, subtraction, multiplication and division are all binary operations.