Any fractional exponent. Keeping the numbers from overflowing is difficult as well. n^5/8 would be n^5 * n^1/8. Raising to the 5th power would require a 512 bit integer and then we would have to implement 1/4 as three square roots. (For the devs out there, we have created a deterministic square root algorithm that is quite fast). We would need dynamic big ints to prevent overflow from strange powers.