9
-20, -14, 28
The next four number in the sequence are... 4,5,5 & 6
21. Add the last 2 numbers to get the next.
That's the Fibonacci sequence! XD They're 21 and 34 if you add up the last two numbers to get the next one.
54
9
The numbers are increasing by 1,4,9,16,25,36.... which are square numbers so the next increase is 49. Making the next number in the sequence 141
43, 1806
Two possible answers spring immediately to mind. First, this sequence appears to be a list of the first five prime numbers; in this case, the next number in the sequence would be 13. Second, the intervals between these numbers comprise the sequence "1 2 2 4", in which the nth number equals the product of the (n-1)th and (n-2)th numbers. Based on this, the next number in the given sequence would be 11 + (4*2) = 19.
This list of numbers is the list of prime numbers. Following 11, the next two numbers in the list are 13 and 17.
3 1.5
possibly 16
15... you're dividing by 2 each time.
46
13, 21 - it is the Fibonacci sequence
392