Seven is the only variety D for which the equation 2n − D = x2 has much more than two remedies for n and x pure. Especially, the equation 2n − seven = x2 is called the Ramanujan–Nagell equation. Against this, if you click a Microsoft-provided ad that seems on https://senioraidtools.com/10-easy-mobility-exercises-for-seniors-to-stay-active-and-independent/