seven is the one range D for which the equation 2n − D = x2 has much more than two remedies for n and x pure. Specifically, the equation 2n − 7 = x2 is recognized as the Ramanujan–Nagell equation. 2 hours back By Mashable Staff A MacBook Professional for $280 is unheard of — so get one particular right before this deal disappears A MacBo