Digit sum

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In mathematics, the digit sum of a given integer is the sum of all its digits, e.g. the digit sum of 84001 is calculated as 8+4+0+0+1 = 13.

This concept is closely related to, but not the same as, the digital root, which is the result of repeatedly applying the digit sum operation until the remaining value is only a single digit - that is the digital sum of any non-zero integer will be a number in the range 1 to 9, whereas the digit sum can take any value.

Digit sums can be used for quick divisibility tests: a natural number is divisible by 3 or 9 if and only if its digit sum (or digital root) is divisible by 3 or 9, respectively.

[edit] External links

• Digit sum at Mathworld.
• Sequence A007953 in the On-Line Encyclopedia of Integer Sequences.
• 2005 Scientia Magna article