Math
Digit Sum Calculator
Add up the digits of a number.
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Sum a number's digits (and reduce to a single-digit root).
The math behind it
Add each digit. The digital root repeats this until one digit remains (equals n mod 9, with 9 for multiples of 9).
Worked Example
12345 → 1+2+3+4+5 = 15, root 6.Frequently Asked Questions
Use?
Divisibility checks (by 3 or 9) and checksum tricks.
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