Comprehensive Calculator Guide
This calculator adds up the digits of any whole number, repeats down to one digit for the digital root, and counts the digits. 9875 sums to 29 with digital root 2. Digit sums test divisibility by 3 and 9, and digital roots check sums and products by casting out nines.
Digit sums and digital roots
The digital root equals the remainder on dividing by 9 (or 9 when that is zero). A number divides by 3 or 9 when its digit sum does.
How to Use
- Enter a positive whole number.
- Nothing else is needed.
- Press “Add the digits” to see the digit sum, digital root and digit count.
Formula Used
Digital root = 1 + (n − 1) mod 9
Practical Examples
- Example 1
- 9875: 29, root 2.
- Example 2
- 123456789: 45, root 9.
Important Tips
- Cast out nines as you go.
- Use it before dividing by 3 or 9.
- Check long multiplication.
Common Mistakes to Avoid
- Confusing digit sum and digital root.
- Using it for 6 or 7 alone.
- Treating a match as proof.
Frequently Asked Questions
- What is a digital root?
- The single digit left after repeated digit sums.
- Divisible by 9?
- If the digit sum is.
- Digital root of 999?
- 9.