What do rational numbers commonly used in fortune telling mean?

The principle in the Book of Changes is explained in this way, that is, using "image, number and principle" to describe nature is a way to simulate the construction of nature, but it is like mathematical principle, not like mathematical principle!

Rationality refers to the objective law of the movement of things, that is, the principle of simplicity.

The number here refers not only to the number of things, but also to the existing state of things in a certain time and space.

In short, people's life span will not exceed 200 years, and 200 is this number.

As for your "fortune-telling theory", I think it is a method to frame (occupy) the development trend of the measured things or people and the specific situation of some specific points (numbers), and infer the reasons (theories) why these situations happen.

For example, the "Heluo number" is to use a series of deduction methods to simulate the fate of a person's life and what may happen at a specific time.

It's time to clarify your question.