Four of the following five are alike in a certain way and so form a group. Which is the one that does not belong to that group ?
(A) : 50 = $$7^2+1$$
(B) : 65 = $$8^2+1$$
(C) : 170 = $$13^2+1$$
(D) : 255 = $$16^2-1$$
(E) : 290 = $$17^2+1$$
=> Ans - (D)
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