7 is the sole number D for which the equation 2n − D = x2 has in excess of two alternatives for n and x purely natural. Specifically, the equation 2n − 7 = x2 is known as the Ramanujan–Nagell equation. two several hours in the past By Mashable Staff https://bathroomgrabbarsforelderl24395.blogoxo.com/38094971/not-known-facts-about-7-day-pill-organizers