  A probability distribution is n-divisible if its nth convolution root exists.
While modeling the dependence structure between several (re)insurance losses by
an additive risk factor model, the infinite divisibility, that is the
$n$-divisibility for all $n \in\mathbb N$, is a very desirable property.
Moreover, the capacity to compute the distribution of a piece (i.e., a
convolution root) is also desirable. Unfortunately, if many useful
distributions are infinitely divisible, computing the distributions of their
pieces is usually a challenging task that requires heavy numerical
computations. However, in a few selected cases, particularly the Gamma case,
the extraction of the distribution of the pieces can be performed fully
parametrically, that is with negligible numerical cost and zero error. We show
how this neat property of Gamma distributions can be leveraged to approximate
the pieces of other distributions, and we provide several illustrations of the
resulting algorithms.
