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

Question

Pattern and sequence problem

Answer 1

3 ((-9)) -6 ((+18)) 12 ((-8)) 4 ((+16)) 20

There are many possibilities- you can always make a more complicated equation to fit any length of starting numbers, but the simplest answer looks like:

See the -9, -8, etc., and the +18, +16, etc.?  Extend that pattern with -7, -6, ... and +14, +12, ... .

3 ((-9)) -6 ((+18)) 12 ((-8)) 4 ((+16)) 20 ((-7)) 13 ((+14)) 27 ((-6)) 21 ((+12)) 33

So the sequence would be:

3, -6, 12, 4, 20, 13, 27, 21, 33

The next number would be:

13