simplifying out negative signs in exponents

edit

Hello all!

I can't for the life of me find a way to force sage to return terms with only positive coefficient variable exponents. For example, if I enter something like

assume(n, 'integer', n>10)
c = 2^(-n)

I would like the output to be something like 1/(2^n), but instead I can only get something like 2^(-n). Is there a way to force the output to display only positive coefficients in front of the n?

In general I'd like some magicFunc function which I could feed some expression g(x,n) and have it return a rational expression with no negatives; eg.

var('x,n')
assume(x,'real')
assume(n,'integer',n>10)
g(x,n) = 2^(-n)*x^(-3*n)*3^n
magicFunc(g(x,n))

Would return 3^n/(2^n*x^(3n))

Is this possible? This seems like it should be an existent simplification method, but nothing I've tried seems to work.

Thanks!