  In recent years there has been an interest in constructing examples of closed
Riemann surfaces whose jacobian varieties are isogenous to a product of many
elliptic factors and some other jacobian varieties. The first ones, provided by
Ekedahl and Serre, are examples for which the isogenous decomposition has all
factors being elliptic curves. It is well known that given two elliptic curves
$E_{1}$ and $E_{2}$, there is a closed Riemann surface $X$ of genus two, with
equations in terms of the elliptic curves, and whose jacobian variety $JX$ is
isogenous to $E_{1} \times E_{2}$. In this paper, given $s \geq 3$ elliptic
curves $E_{1},\ldots, E_{s}$, we provide an explicit construction of a closed
Riemann surface $X$ of genus $g=1+2^{s-2}(s-2)$, with $JX$ isogenous to $E_{1}
\times \cdots \times E_{s} \times A$, where $A$ is the product of some elliptic
curves and jacobian varieties of hyperelliptic Riemann surfaces, all of them
explicitly in terms of the given elliptic curves. In particular, for $s=3$,
this provides explicit Riemann surface of genus three whose jacobian variety is
isogenous to $E_{1} \times E_{2} \times E_{3}$, for given elliptic curves.
