7 is the only real number D for which the equation 2n − D = x2 has a lot more than two answers for n and x normal. Especially, the equation 2n − seven = 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 adore with Odysseus and promised him immortality