The formula.....................gives the maximum number of electrons that can be found in a shell. where "n" denotes the orbital number or energy level index, and "1, 2, 3,...

The formula 2n², where "n" is the orbit number or energy level index, 1, 2, 3,... gives the maximum number of electrons that can be found in a shell. This electron number is also taken as the valence electrons number which is the number of electrons in the outermost shell.