What number is next in the sequence? 3, -6, 12, 4, 20

Answer 1

The next number is 13.

There are two patterns. The first pattern is for the n₂ and every other number, subtract by an increase in 1 of the initial each time. The second pattern is for n3, add 18 to the precceding number. For every other number, reduce the number by two from the preceding number. I know this explantion is wordy and confusing. I have added the figure to explain this:

3 subtract -9

-6 add 18

12 subtract -8

4 add 16

20 subtract -7

13