The information given in those 3 terms isn't enough to uniquely determine the rule.
I've just found three different rules that all generate 11 .. 12 .. 16 .. , and each one
produces a different 4th term.
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11
15
The answer depends on the question. One possible question is what is the next number. And one possible answer to that question is 11.
The next is 3.
The next number in this sequence should be 33.