13, 29, 15, 26, 17, 23, 19, ?, ?
21, 23
20, 21
20, 17
25, 27
22, 20
13, 29, 15, 26, 17, 23, 19, ?, ?
It is the combination of two series at alternate positions. First series follows the pattern of +2 like 13+2=15, 15+2=17 and so on. Second series follows the pattern of -3 like 29-3=26, 26-3=23 and so on.
So, at the end, 23-3=20 and 19+2=21.