No stable nuclides have a neutron number of 19, 21, 35, 39, 45, 61, 89, 115, 123, or ≥ 127. There are 6 stable nuclides and one radioactive primordial nuclide with neutron number 82 (82 is the neutron number with the most stable nuclides, since it is a magic number): barium-138, lanthanum-139, cerium-140, praseodymium-141, neodymium-142, and samarium-144, as well as the radioactive primordial nuclide xenon-136, which decays by a very slow double beta process. Except 20, 50 and 82 (all these three numbers are magic numbers), all other neutron numbers have at most 4 stable nuclides (in the case of 20, there are 5 stable nuclides S, Cl, Ar, K, and Ca, and in the case for 50, there are 5 stable nuclides: Kr, Sr, Y, Zr, and Mo, and 1 radioactive primordial nuclide, Rb). Most odd neutron numbers have at most one stable nuclide (exceptions are 1 (H and He), 5 (Be and B), 7 (C and N), 55 (Mo and Ru) and 107 (Hf and Ta)). However, some even neutron numbers also have only one stable nuclide; these numbers are 0 (H), 2 (He), 4 (Li), 84 (Ce), 86 (Nd) and 126 (Pb), the case of 84 is special, since Ce is theoretically unstable to double beta decay, and the nuclides with 84 neutrons which are theoretically stable to both beta decay and double beta decay are Nd and Sm, but both nuclides are observed to alpha decay. (In theory, no stable nuclides have neutron number 19, 21, 35, 39, 45, 61, 71, 83–91, 95, 96, and ≥ 99) Besides, no nuclides with neutron number 19, 21, 35, 39, 45, 61, 71, 89, 115, 123, 147,... are stable to beta decay (see Beta-decay stable isobars).