seven is the one amount D for which the equation 2n − D = x2 has in excess of two methods for n and x normal. Specifically, the equation 2n − 7 = x2 is referred to as the Ramanujan–Nagell equation.The island of Ogygia was the house of The attractive nymph named Calypso. She fell madly in really like with Odysseus and promised him immortality