seven is the one quantity D for which the equation 2n − D = x2 has more than two solutions for n and x organic. Particularly, the equation 2n − 7 = x2 is recognized as 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 Ever