For a one-off implementation of your typesetting needs, you could try
This will work in both text and math mode. If you use the
amsmath package, you should type
as this is slightly more general than the first solution. Specifically, it'll work better if the expression ever occurs in scriptstyle (first-level sub- and superscripts) or scriptscriptstyle (second-level sub- and superscripts) material.
Conversely, if you have a lot of numbers that you wish to typeset in this way, you should implement a solution along the lines provided in @AlfC's answer. Otherwise, sooner or later some inconsistencies in the way you typeset these numbers will creep in.