Question: Terfenol-D is an alloy that contains a chemical element with an atomic number of what?

Context paragraphs:
List of countries by manganese production: Manganese is a chemical element that is designated by the symbol Mn and has an atomic number of 25.  It is found as the free element in nature (often in combination with iron), and in many minerals.  The free element is a metal with important industrial metal alloy uses.  Manganese ions are variously colored, and are used industrially as pigments and as oxidation chemicals.  Manganese (II) ions function as cofactors for a number of enzymes; the element is thus a required trace mineral for all known living organisms.

Atomic number: The atomic number or proton number (symbol Z) of a chemical element is the number of protons found in the nucleus of an atom.  It is identical to the charge number of the nucleus.  The atomic number uniquely identifies a chemical element.  In an uncharged atom, the atomic number is also equal to the number of electrons.

Dysprosium: Dysprosium is a chemical element with symbol Dy and atomic number 66.  It is a rare earth element with a metallic silver luster.  Dysprosium is never found in nature as a free element, though it is found in various minerals, such as xenotime.  Naturally occurring dysprosium is composed of seven isotopes, the most abundant of which is Dy.

Unbiunium: Unbiunium, also known as eka-actinium or element 121, is the hypothetical chemical element with symbol Ubu and atomic number 121.  "Unbiunium" and "Ubu" are the temporary systematic IUPAC name and symbol, until a permanent name is decided upon.  In the periodic table of the elements, it is expected to be the first of the superactinides, and the third element in the eighth period: analogously to lanthanum and actinium, it could be considered the fifth member of group 3 and the first member of the fifth-row transition metals.  It has attracted attention because of some predictions that it may be in the island of stability, although newer calculations expect the island to actually occur at a slightly lower atomic number, closer to copernicium and flerovium.

Pseudo palladium: Pseudo palladium (RhAg) is a binary alloy consisting of equal parts of rhodium (atomic number 45) and silver (atomic number 47) created using nanotechnology to create a far more homogenous mixture than might be possible using more conventional methods.  This alloy exhibits properties of the intervening element palladium (atomic number 46).

Manganese: Manganese is a chemical element with symbol Mn and atomic number 25.  It is not found as a free element in nature; it is often found in minerals in combination with iron.  Manganese is a metal with important industrial metal alloy uses, particularly in stainless steels.

Unbinilium: Unbinilium, also known as eka-radium or simply element 120, is the hypothetical chemical element in the periodic table with symbol Ubn and atomic number 120.  "Unbinilium" and "Ubn" are the temporary systematic IUPAC name and symbol, until a permanent name is decided upon.  In the periodic table of the elements, it is expected to be an s-block element, an alkaline earth metal, and the second element in the eighth period.  It has attracted attention because of some predictions that it may be in the island of stability, although newer calculations expect the island to actually occur at a slightly lower atomic number, closer to copernicium and flerovium.

Terfenol-D: Terfenol-D, an alloy of the formula Tb Dy Fe (x ~ 0.3), is a magnetostrictive material.  It was initially developed in the 1970s by the Naval Ordnance Laboratory in United States.  The technology for manufacturing the material efficiently was developed in the 1980s at Ames Laboratory under a U.S. Navy funded program.  It is named after terbium, iron (Fe), Naval Ordnance Laboratory (NOL), and the D comes from dysprosium.

Mass number: The mass number (symbol "A"), also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus.  It determines the atomic mass of atoms. Because protons and neutrons both are baryons, the mass number A is identical with the baryon number B as of the nucleus as of the whole atom or ion.  The mass number is different for each different isotope of a chemical element.  This is not the same as the atomic number ("Z") which denotes the number of protons in a nucleus, and thus uniquely identifies an element.  Hence, the difference between the mass number and the atomic number gives the number of neutrons ("N") in a given nucleus: "N=A−Z".

Moseley's law: Moseley's law is an empirical law concerning the characteristic x-rays that are emitted by atoms.  The law was discovered and published by the English physicist Henry Moseley in 1913.  It is historically important in quantitatively justifying the conception of the nuclear model of the atom, with all, or nearly all, positive charges of the atom located in the nucleus, and associated on an integer basis with atomic number.  Until Moseley's work, "atomic number" was merely an element's place in the periodic table, and was not known to be associated with any measureable physical quantity.  Moseley was able to show that the frequencies of certain characteristic X-rays emitted from chemical elements are proportional to the square of a number which was close to the element's atomic number; a finding which supported Van den Broek and Bohr's model of the atom in which the atomic number is the same as the number of positive charges in the nucleus of the atom.  In brief, the law states that the square root of the frequency of the emitted x-ray is proportional to the atomic number.

Supporting paragraphs: Terfenol-D Dysprosium
Answer: 66