One possibility is 17. The pattern that justifies it is the following.
The first three numbers of the sequence are 5, 11 and 17. The sequence increases by 6 every 3rd number from the first number. The sequence increases by 2 every 3rd number from the second number. The sequence increases by 6 every third number from the third number.
This makes the sequence 5,6,11,11,8,17,17,10,23,23,12,29,29,14...continuing the described patterns.