Nuclei with the same number of protons but a different number of neutrons are called isobars
Nuclei with the same number of neutrons but a different atomic number are called isotopes
Nuclei with the same mass number are called isotones
Nuclei with the same number of protons (same atomic number) and a different number of neutrons are called Isotopes. These nuclei belong to the same element as the atomic number remains the same.
Nuclei with the same number of neutrons but a different number of protons (different atomic number) are called isotones.
Nuclei with the same mass number that is the same "sum of neutrons and protons" are called isobars.