Sequences And Series

Let \(a_1, a_2, a_3, \ldots\) be in an arithmetic progression of positive terms.

Let \(A_k=a_1^2-a_2^2+a_3^2-a_4^2+\ldots+a_{2 k-1}^2-a_{2 k}^2\).

If \(\mathrm{A}_3=-153, \mathrm{~A}_5=-435\) and \(\mathrm{a}_1^2+\mathrm{a}_2^2+\mathrm{a}_3^2=66\), then \(\mathrm{a}_{17}-\mathrm{A}_7\) is equal to ________.