Answer:
21
Step-by-step explanation:
0 + 1 = 1
1 + 2 = 3
3 + 3 = 6
6 + 4 = 10
10 + 5 = 15
15 + 6 = 21
Each number is added to an increase of 1 - first add 1, then add 2, then add 3,etc
Not listed but next would be 21 + 7 = 28
so it would be 0, 1, 3, 6, 10, 15, 21, 28
