The rare earths are a group of 17 elements comprising Scandium, Yttrium, and the Lanthanides. The Lanthanides are a group of 15 (Cerium, Dysprosium, Erbium, Europium, Gadolinium, Holmium, Lanthanum, Lutetium, Neodymium, Praseodymium, Samarium, Terbium, Thorium, Thulium, Ytterbium) chemically similar elements with atomic numbers 57 through 71, inclusive.