The next number is -21
The next number in the sequence 3-15-6-30-21 is -207.
291
21: (3)+3=(6)+4=(10)+5=(15)+6=(21)
It is: 21
The next number is -21
28
15
55
The next number in the sequence 3-15-6-30-21 is -207.
21
24
291
the answer will be 21
24
21: (3)+3=(6)+4=(10)+5=(15)+6=(21)
It is: 21