"""Returns the order of ``a`` modulo ``n``. The order of ``a`` modulo ``n`` is the smallest integer ``k`` such that ``a**k`` leaves a remainder of 1 with ``n``.

This hangs trying to factor the 891-bit integer p 2 - 1, which is longer than the longest solved RSA Challenge number. (As it happens, the hard part of this factorization is a 675-bit integer which is ...