Seven is the sole quantity D for which the equation 2n − D = x2 has more than two options for n and x organic. Particularly, the equation 2n − 7 = x2 is named the Ramanujan–Nagell equation. Jahannam has 7 gates which are open up all of the time. https://senioraidtools.com/10-easy-mobility-exercises-for-seniors-to-stay-active-and-independent/