3 c - 16*c
c^3 - 16*c
/ 2\ c*\-16 + c /
c*(-16 + c^2)
(c + 4)*c*(c - 4)
((c + 4)*c)*(c - 4)
c*(-4 + c)*(4 + c)
c^3 - 16.0*c