Separating the terms into three groups of three gives (2, 9, 11), (3, 10, 13) and (4, 11, 16). The rule is that the sum of the first two terms equals the third term, meaning 2 + 9 = 11, 3 + 10 = 13 and 4 + 11 = 15. Since the series gives 16 instead of 15, 16 is the wrong term.