All problems like this are invalid. Any number next would make a valid sequence.
If there is nothing in the statement of the problem about what kind of sequence it is, then there can be no "right" answer.
In every problem like this, there are many possible patterns that produce the given sequence of numbers; the different patterns can produce very different next numbers.
Spend as much (or as little!) time as you want trying to find a logical pattern to the given numbers -- knowing that any answer you find might not be the "right" answer.
