|If you actually want it done within the column itself, you'll need a macro.|
If you are willing to perform a couple of extra steps then you can accomplish the same thing with a single formula and a couple of Editing commands.
I'll assume your numbers start in A1...adjust my suggested formula as required:
In Row 1 of some other column, enter this formula and drag it down:
Now select the new values and do an Edit...Copy (CTRL - C)
Select the first cell of the original values and do an Edit...PasteSpecial...Values
Finally, delete the values created by the formula.