Coefficients of a polynomial defined by its roots : pcoeff pcoef

pcoeff (or pcoef) takes as argument a list of the roots of a polynomial P.
pcoeff (or pcoef) returns a univariate polynomial having these roots, represented as the list of it's coefficients by decreasing order.
Input :

pcoef([1,2,0,0,3])

Output :

[1,-6,11,-6,0,0]

i.e. (x - 1)(x - 2)(x2)(x - 3) = x5 - 6x4 + 11x3 - 6x2.