I know this is old, but maybe what I say might help other ppl too, so its for the greater cause.

Getting a single digital root, by itself, is too simple to actually use a software and I will always advocate knowing how to do it yourself on paper before using third-party solutions. But depending on the situation, like when you are trying to solve a puzzle consisting of many numbers, and you would like to check if their digital root has any meaning, a little extensive endeavor for what could prove to only be just a hunch, so you may save time and effort by using something as simple as an excel spreadsheet

I know not everyone has the luxury of being able to buy Excel, but openoffice.org offers a free alternative (and I believe they have a port for Mac OS-X users). Basically, any spreadsheet program that has the MOD() function will do the trick (MOD stands for Modulo, a well known operator and/or function to programmers... may be less known to the common mortal though).

As a very basic example, lets say you put the number you wanna get the digital root for in the A1 field and get its digital root to appear in the B1 field, edit the B1 field and put the following string: =IF(MOD(A1; 9)=0;9;MOD(A1; 9))

*Explanation of the above formula (for those who really want to know):*

The MOD function will give you the REST of a the division of A1 by 9. (i.e. 12 divided by 9 would be 3 because you can fit 9 only once in 12 and 12-9 = 3).

If you calculate the digital root of 12 manually... you get 1+2 = 3.

The MOD function will return the right digital root for all numbers except... a number divisible by 9 since the rest would be 0 (i.e. 9 fits once into 9 therefore there is 0 rest for this division).

This is where the IF comes in. IF the result of MOD(A1; 9) is 0, than its digital root is 9. Take 18 for example. 18 divided by 9 has 0 rest since the result is 2 (9x2=18). But the digital root of 18 is 1+8=9.Now once that is done, youll be able to do this for many numbers by entering all your numbers in the A column (A1, A2, A3, A4 etc..) and just drag and extend the B1 field to the last number in the A column (if you last number is located in A4, then drag and extend the B1 field to B4).

This will prove useful for any number ABOVE 0. When dealing with negative numbers, depending on how the MOD function was implemented in the spreadsheet, it may or may not give the right answer, so the best way to handle it is to treat it as if it was a positive number.