1, 3, 15, 105, what's next?

Problem solving process:

3÷ 1=3

15÷3=5

105÷ 15=7

That is to say, the number obtained by dividing two adjacent digits is arithmetic progression, so we can know from this law that 105X9=945.

Solution ideas 1. When seeking the law of series, we can first consider whether the relationship between numbers is square or cubic. Mastering this rule requires a certain degree of proficiency in numbers in daily life.

2. Another method is to find out the relationship between two adjacent numbers, such as addition, subtraction, multiplication and division of adjacent numbers, so that it is possible to get related numbers, and according to the law, we can know what the next digit is.

3. The calculation process must be accurate and there must be no mistakes, otherwise you still can't find the direction under the correct thinking.