What is the missing number of the following sequence - 5, 39, 8, 9, 40, 11, 13, 27, 14, 15, ??, 17

Answer 1

5, 39, 8, 9, 40, 11, 13, 27, 14, 15, ......, 17
(5, 39, 8), (9, 40, 11), (13, 27, 14), (15, ......, 17)
a b c
b = c^2 - a^2
8^2-5^2 = 64-25 = 39
11^2-9^2 = 121-81 = 40
14^2-13^2 = 196-169 = 27
Similarly
17^2-15^2 = 289-225 = 64

Answer 2

Middle number is difference between the square of its successor and predecessor.
8^2-5^2=64-25=39

11^2-9^2=121-81=40

14^2-13^2=196-169=27

17^2-15^2=289-225=64

so answer is 64