Originally posted by doodinthemood
As far as I considered it, cube root is a function, not a number, because 3 isn't involved anywhere in the process. If it isn't allowed you should also not allow percentages.
Incorrect, the function would be the third root of the base (in this case 8) or 8 to the power of one-third. In both cases, an extra digit is required in order to complete the expression, otherwise it is meaningless. Square-root, although technically has a two, can also be written without any numbers.
Percentage is a tricky one, but has a widely accepted symbol, however that symbol is also used for the modulus operation in some situations. In the percentage form, the o's in the percentage represent the 0's from the 100, so dood might have a point there.
But if we are going to be this picky anyway, the negative sign cannot be used because it creates a new number. -(2) is actually -1 x 2 so we are introducing a new number -1. -2 is not the same as -(2) if we are using specific digits.