**Root sum**

Basically take the sum of the 6 numbers, then add the numbers making up the sum. For example, for a sum of 124, the root sum is 7 (1+2+4) and for a sum of 198, the root sum is 9 (1+9+8 = 18 and 1+8 = 9). The root sum can take any number from 1 to 9, never 0.

For all 13,983,816 combinations, root sums of 3, 6 and 9 happen 1,553,784 times each and root sums of 1, 2, 4, 5, 7 and 8 happen 1,553,744 times each. Basically, 11.11% in each case.