seven is the sole quantity D for which the equation 2n − D = x2 has in excess of two methods for n and x pure. Particularly, the equation 2n − seven = x2 is named the Ramanujan–Nagell equation. The island of Ogygia was the house of The gorgeous nymph named Calypso. She fell madly in love with Odysseus and promised him immortality and Everl