I have removed all old versions of the documentation from
docs.sympy.org.
docs.sympy.org now only serves the documentation for
the latest release and the development version, and will serve only
those two going forward. Links with old versions now redirect to the
latest docs (this only works if the page still exists in the latest
docs, otherwise it will give a 404).
If you want to access old versions of the documentation, I recommend
downloading the respective zip file from
https://github.com/sympy/sympy/releases. However be aware that the
SymPy development community generally does not support versions older
than the latest (currently 1.5.1).
Note that the mpmath documentation, which used to be served as part of
some old SymPy versions' docs, can be found at
http://mpmath.org/doc/current/index.html
Aaron Meurer