TITLE: The complexity of the leading fractional bit of a power of a rational number
QUESTION [11 upvotes]: On a mailing list (math-fun) that I subscribe to Dan Asimov asked what's the most efficient way to calculate the leading decimal digits (say 10 of them) of $(p/q)^n \bmod 1$ where $p$ and $q$ are fixed (think of $p/q = 3/2$) and $n$ varies.  There were a number of suggestions, but all of them clearly had complexity proportional to $n$.  So my question is, for concreteness, let $b(n) = \lfloor 2(3/2)^n \rfloor \bmod 2$ (the leading fractional bit of $(3/2)^n$).  Suppose that $n$ is specified in binary.  What is the complexity (both time and space) of calculating the function $b(n)$?  After thinking about it for a while I wouldn't be surprised if it's exp-space hard.  Does anyone know anything about this?

REPLY [4 votes]: From the review of 
Mika Hirvensalo, Juhani Karhumäki, and Alexander Rabinovich, Computing partial information out of intractable: powers of algebraic numbers as an example,  J. Number Theory 130 (2010), no. 2, 232–253, MR2564895 (2010j:11117), it looks like there may be something of interest there.