Let the four consecutive odd numbers be (2x – 3), (2x – 1), (2x + 1) and (2x + 3) ∴ Their product = (2x - 1) (2x + 1) (2x - 3) (2x + 3) =(4x2−1)(4x2−9) =16x4−40x2+9 =(4x2−5)2−16 Hence, on adding 16, the result will be a perfect square.