Let w ( n , g ) be the number of ways of distributing n particles among the g sublevels of an energy level. There is only one way of distributing n particles with one sublevel, therefore w ( n , 1 ) = 1 . It is easy to see that there are ( n + 1 ) ways of distributing n particles in two sublevels which we will write as: w ( n , 2 ) = ( n + 1 ) ! n ! 1 ! .