21
since the difference between each number is as in the order of the given pattern.
so you add 13+8=21
The next number is -21
the answer will be 21
10
225
This is the series of square numbers, (16= 4*4). The next number is 5*5=25.
21
21
21.
21
The next number is 25 but there are the sequence is infinite so there can be no end to the sequence.
A single number, such as 12848384 does not make a series.
12,14,16,18,20,22,24,26,28,30,32,34,36,38,40,42,44,46,48,50