7 is the sole selection D for which the equation 2n − D = x2 has greater than two options for n and x normal. Especially, the equation 2n − 7 = x2 is named the Ramanujan–Nagell equation. The island of Ogygia was the home of The gorgeous nymph named Calypso. She fell madly in enjoy with Odysseus and promised him immortality and Everlasting