But is the significant digits that is the issue here. Internally 1/30! is held as 3.7699876 *10^-33 (or something like that) whereas your value for e is held as 2.7182818*10^0 (or there about) for the computer to add one to the other it requires them to be of the same base. When it converts 1/30! to base 10^0 it will lose all of the digits because it can only hold 18 digits at base 10.

Your answer is shown to more than 18 digits because of the conversion from base 2 (the internal representation) and base 10 (the representation of the number on your screen).

This is a fundamental characteristic of floating point numbers. I hope that my explanation helps.

graeme.