The maximum number of electrons found on energy levels one through six are two, eight, 18, 32, 50 and 72. The formula for determining the number of electrons is two multiplied by n squared, or 2n^2.
The energy levels are typically referred to by their shell number rather than their energy level. In ascending order, the shell letters are K, L, M, N, O, P and Q. Generally, due to the attraction between electrons and the nucleus, the electrons fill the inner shells before filling in the outer shells. The outermost shell occupied by electrons is known as the valence shell.