Try the documentation Math blocks
and http://www.appinventor.org/bookChapters/chapter18.pdf
perhaps something like this if ! is not a factorial symbol
depending on what you mean by
(1/3%)^5! for example 1/3 percent or 33 percent or whatever.
The Math Blocks does not have a factorial or percentage operator.
An alternative to Math Blocks is App Inventor Extensions: Math Parser