Look at pic and find whats next

Hi,
49 - 9 = 40
40 - 7 = 33
33 - 5 = 28
28 - 3 = 25
25 - 1 = 24
Explanations :
9-2 = 7
7-2 = 5
5-2 = 3
3-2 = 1
✅(•‿•)