There are a variety of possible next numbers. As long as the pattern you find is consistent with the present numbers, you can justify the choice for the next number.
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.
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