Application Of Derivatives

Let the set of all values of \(p\), for which \(f(x)=\left(p^2-6 p+8\right)\left(\sin ^2 2 x-\cos ^2 2 x\right)+2(2-p) x+7\) does not have any critical point, be the interval \((a, b)\). Then \(16 a b\) is equal to _________.