28
Without a sequence given in the question, the next number to 6 is 7.
3
The next number in the sequence 3-15-6-30-21 is -207.
The next is 3.
28
35
Without a sequence given in the question, the next number to 6 is 7.
3
44
The next number in the sequence will be 56.
The next number in the sequence 3-15-6-30-21 is -207.
The next is 3.
The nest number in the sequence is 18. Note that the difference between each number and the next number in the sequence follows the simple sequence of 1,2,3,4. Obviously the next in the sequence of increases is 5, so 13+5=18.
19
The next number in the sequence is 18. It's +1, +2, +3, +4, ....
6