The root of all digits
The digital root (also repeated digital sum) of a non-negative integer is the (single digit) value obtained by an iterative process of summing digits, on each iteration using the result from the previous iteration to compute a digit sum. The process continues until a single-digit number is reached.
For example, the digital root of \(487\) is \(1\):
What is the digital root of \(123,456,\ldots,497,498,499,500\)?
Note: The number above is a base 10 number in which the digits are formed from consecutive integers from 1 to 500.