7 is the one quantity D for which the equation 2n − D = x2 has over two solutions for n and x purely natural. In particular, the equation 2n − 7 = x2 is known as the Ramanujan–Nagell equation. Jahannam has seven gates that are open always. (Qur’an – https://best-pool-exercise-equipm54837.vblogetin.com/43785796/the-2-minute-rule-for-7-day-pill-organizers