7 is the one number D for which the equation 2n − D = x2 has a lot more than two answers for n and x purely natural. Specifically, the equation 2n − seven = x2 is known as the Ramanujan–Nagell equation. We have been introducing additional all the time. https://mobility-exercises-for-se39197.robhasawiki.com/11686131/considerations_to_know_about_7_day_pill_organizers