Question

Consider y=n^2, then the expression simplifies to
(y2−10y+24)(y2−9y+18)

which can be readily factorized.
Any common factor (such as (y-6)) can be cancelled provided that we specify the restriction that (y-6) ≠ 0, or equivalently n2≠0, or n≠0. The factors that are left will be the answer.