[The documentation states][1]:

> N does not raise the precision of approximate numbers in its input


`163.0` (or `163.`, or ``163` ``) is a machine precision number, and *Mathematica* will not fake a higher precision when a certain number of digits are requested with `N`.

See [this answer][2] and [this tutorial][3] for more.

These questions may also be of interest:

https://mathematica.stackexchange.com/q/7564/121

https://mathematica.stackexchange.com/q/3736/121




  [1]: http://reference.wolfram.com/mathematica/ref/N.html#570568123
  [2]: https://mathematica.stackexchange.com/a/3153/121
  [3]: http://reference.wolfram.com/mathematica/tutorial/NumericalPrecision.html