Cound one give examples of irrational algebraic function that can be expanded as infinite series with unbounded positive integral coefficients, like:
$$f(x)=\sum_0^{\infty}a_i x^i,\qquad a_i\in \mathbb{N} \cup \{0\}$$
I post the question for interest, since the first time it has not been clearly expressed, I have updated the question.
$$\frac{1 - \sqrt{1 - 4x}}{2x} = \sum_{k=0}^\infty C_n x^n$$ where $C_n$ are the Catalan numbers.
There are many other examples in the OEIS.