Natural Logarithm (Wolfram MathWorld)

The natural logarithm lnx is the logarithm having base e, where e=2.718281828.... (1) This function can be defined lnx=int_1^x(dt)/t (2) for x>0. This definition means that e is the unique number with the property that the area of the region bounded by the hyperbola y=1/x, the x-axis, and the vertical lines x=1 and x=e is 1. In other words, int_1^e(dx)/x=lne=1. (3) The notation lnx is used in

Log (Mathematica)

http://reference.wolfram.com/mathematica/ref/Log.html