You could put any number next and it would be a valid sequence.
And if you see a logical pattern in the numbers that leads logically to a next number in the sequence, it still might not be the "right" pattern that the originator of the problem used.
There is no useful mathematics in any problem like this. Spend a minute or two at the most looking for a POSSIBLE answer; then move on and find something more useful to do with your time.
