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The digit sum - add the digits of the representation of a number in a given base. For example, considering 84001 in base 10 the digit sum would be 8 + 4 + 0 + 0 + 1 = 13. The digital root - repeatedly apply the digit sum operation to the representation of a number in a given base until the outcome is a single digit. For example, considering ...
The decimal digital root 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 and digital roots 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.
The additive persistence counts how many times we must sum its digits to arrive at its digital root. For example, the additive persistence of 2718 in base 10 is 2: first we find that 2 + 7 + 1 + 8 = 18, then that 1 + 8 = 9. There is no limit to the additive persistence of a number in a number base .
011 (3) 100 (4) 101 (5) --- 010 (2) is the binary digital sum of 3, 4 and 5. The binary digital sum is crucial for the theory of the game of Nim . The digital sum in base b is an associative and commutative operation on the natural numbers ; it has 0 as neutral element and every natural number has an inverse element under this operation.
The additive persistence of 2718 is 2: first we find that 2 + 7 + 1 + 8 = 18, and then that 1 + 8 = 9. The multiplicative persistence of 39 is 3, because it takes three steps to reduce 39 to a single digit: 39 → 27 → 14 → 4. Also, 39 is the smallest number of multiplicative persistence 3.
Since four bits (2 4) can hold 16 values, this means hexadecimal (hex) digits can be represented by four bits too. [23] Since there are a limited number of segments in seven-segment displays, a couple of the hexadecimal digits are required to be displayed as lowercase letters, otherwise the uppercase letter "B" would be the same as the digit "8 ...
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Logarithmic number systems have been independently invented and published at least three times as an alternative to fixed-point and floating-point number systems. [1] Nicholas Kingsbury and Peter Rayner introduced "logarithmic arithmetic" for digital signal processing (DSP) in 1971. [2]