The next number in the series 20 23 28 14 17 22 11?

Beginning with the 20, the set of rules to get the next 3 terms is:

Add 3 . . . . . 23

Add 5 . . . . . 28

Take half. . . 14

Add 3 . . . . . 17

Add 5 . . . . . 22

Take half. . . 11

Next comes:

Add 3 . . . . . 14

Add 5 . . . . . 19