7 is the sole range D for which the equation 2n − D = x2 has in excess of two answers for n and x organic. In particular, the equation 2n − 7 = x2 is referred to as the Ramanujan–Nagell equation.The island of Ogygia was the house of the beautiful nymph named Calypso. She fell madly in appreciate with Odysseus and promised him immortality and