The divisors of a polynomial : divis

divis takes as argument a polynomial (or a list of polynomials) and returns the list of the divisors of the polynomial(s).
Input :

divis(x^4-1)

Output :

[1,x^2+1,x+1,(x^2+1)*(x+1),x-1,(x^2+1)*(x-1),

(x+1)*(x-1),(x^2+1)*(x+1)*(x-1)]

Input :

divis([x^2,x^2-1])

Output :

[[1,x,x^2],[1,x+1,x-1,(x+1)*(x-1)]]