Because these numbers conform to the laws of n 3-1 (when n is even 0,2,4) and n 3+1(when n is odd1,3,5).

Finding the law is the basic skill of primary school mathematics and middle school mathematics teaching, and the purpose is to let students experience and explore the simple arrangement law of figures and numbers.

Extended data:

General functions:

The significance of finding the law to fill in the blanks is actually to strengthen the understanding of the general law of sequence. Although it has many solutions, it is mainly to cultivate your ability to find the general law of series and guess the general term of series (that is, the ability to use incomplete induction), so that when you encounter some series that are difficult to find the general term by general methods, you can guess the general term formula of this series quickly and accurately through the first few terms.

Sequence is a function with positive integer set (or its finite set) as its domain, and it is an ordered number. Every number in a series is called an item in this series. The number ranked first is called 1 item of this series (usually also called the first item), the number ranked second is called the second item of this series, and so on, and the number ranked n is called the n item of this series, usually represented by an.

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