The problem is that you entered 2.5 as a machine precision number, so you are only going to get machine precision output. The way to get high precision output is to start with the exact 5/2 instead of the machine precision 2.5.
In general, you should enter numbers into Mathematica exactly whenever possible. Enter rational numbers as fractions, and don't use decimal approximations for numbers like Pi or Sqrt. Just put them in exactly, and then you can use N to get the output to whatever precision you want.
Helen Read University of Vermont
On 2/17/2013 4:08 AM, Blaise F Egan wrote: > I am trying to evaluate 2.5^125 to high precision. > > R gives 5.527147875260445183346e+49 as the answer but Mathematica > with N[2.5^125,30] gives 5.52715*10^49 and says that is to machine precision.> > I am inexperienced at Mathematica. Am I doing something silly? > > Blaise >