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A lanthanide (sometimes abbreviated as Ln) is element lanthanum (atomic number 57) or one of the 14 following elements, through atomic number 71. Their isotopes have mass numbers in the 130 to 180 range. Lanthanides are trans-iron elements, created by the r-process or s-process or other processes that produce trans-iron elements. Lanthanides make up the bulk of the rare earth elements.