Wikipedia gives here the following formula for the exponential of a formal power series:
$\exp \Big[\ \sum_{n=1}^\infty \frac{a_n}{n!} x^n\ \Big] = \sum_{n=0}^\infty \frac{B_n(a_1,\dots,a_n)}{n!} x^n$
where $B_n$ are (complete) Bell-polynomials. Can anybody give me a ("standard") reference for this?