0, 1, 2, 4, 6, 9, 12, 16, ?
What number should replace the question mark?
Note
Add 1, 1, 2, 2, 3, 3, 4, 4 in the 0, 1, 2, 4, 6, 9, 12, 16 series to find out the next number. For example:
0 + 1 next number is 1
1 + 1 next number is 2
2 + 2 next number is 4
4 + 2 next number is 6
6 + 3 next number is 9
9 + 3 next number is 12
12 + 4 next number is 16
16 + 4 next number is 20.