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What is the sum of digits in a number? (Definition)

The sum of the digits of a number is the addition of each digit composing a number.

A number is made up of digits. In the decimal base, there are 10 digits: 0,1,2,3,4,5,6,7,8 and 9.

How to calculate the sum of digits in a number?

The only method is to count the sum total of all digits, as does dCode.

Example:123 $ 1+2+3 = 6 $

Pay attention to say sum of the digits of a number (the expressions such as the sum of a digit, or the sum of a number are meaningless)

How to calculate a digital root?

The digital root is computed through recursive reduction (repeated sum) that consists in repeating the addition operation until the result has only one digit.

Example:789: $ 7+8+9 = 24 $ and $ 2+4 = 6 $

A mathematical formula makes it possible to calculate the numerical root $ r $ directly: $$ r(n) = n - 9 \left\lfloor \frac{n}{9} \right\rfloor $$

What is the difference between a number and a digit?

A number is made of digits, like a word is made of letters.

Example: There are only 10 digits: 0,1,2,3,4,5,6,7,8,9 (in base 10)

Example: There is an infinity of numbers

Numbers can have only one digit such as 1, 2 ou 3 (they are both numbers and digits)

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