28
The next composite number after 20 is 21.
the next number is 21 because it is adding the last number stated.
The next number will be 13+21 = 34
The next number in the sequence 3-15-6-30-21 is -207.
If you mean: 1 1 2 3 5 8 13 21 then the next number is 13+21 = 34
The next number is -21
31
a
111221
63
26
21