All stable nuclides were listed in two tables for classifying their isotopes in each element with an odd atomic number or with an even atomic number, separately.
Based on these data, it has been reconfirmed that there exist quite a different characteristics on the stable nuclides, depending on the combination of odd or even number of protons (atomic number) and odd or even number of neutrons.
By investigating those known characteristics, an interesting and remarkable regularity on all stable nuclides with odd mass number was recognized that there must be only a single stable nuclide for every odd mass number 1-209, as shown in Table 3. The only exception is that there is no nuclide with the mass number 5 and samarium with the mass number 147 is regarded as being radioactive.