Chemical element isotopes: specifically the elements without any stable isotopes are technetium (atomic number 43), promethium (atomic number 61), and all observed elements with atomic numbers greater than 82. Of the 80 elements with at least one stable isotope, 26 have only one single stable isotope. The mean number of stable isotopes for the 80 stable elements is 3.1 stable isotopes per element. The largest number of stable isotopes that occur for a single element is 10 (for tin, element 50). The mass number of an element, "A", is the number of nucleons (protons and neutrons) in the atomic nucleus. Different isotopes
SN 2002cx brightness faster than SN 1991T and SN 2000cx in the B-band. In the V-band SN 2002cx is similar to SN 1999ac until 30 days after max. Again SN 2002cx declines faster in the V-band than SN 1991T, but slower than is typical for a type Ia. SN 2002cx is peculiar in the R-band, as it brightens very fast in a manner wholly different from SN 1999ac. It has no secondary maximum in R-band as expected if it were similar to SN 1991T, but instead has a plateau after max. The R-band also declines more slowly than normal. The I-band behaves