One possible answer is 4, using the formula:
t(n) = (-n3 + 9n2 - 14n + 78)/6, for n = 1, 2, 3, ...
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11, -10, 9
15
23
There really is no way of telling, but my guess is 22.
There are some solutions where the sequence goes ... 14, 15, 13, ... but since yours goes ...,14, 1, 5, 13, ... it is not clear what the solution is.