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Casting out nines is any of three arithmetical procedures: [1] Adding the decimal digits of a positive whole number , while optionally ignoring any 9s or digits which sum to 9 or a multiple of 9.
The next number in the sequence (the smallest number of additive persistence 5) is 2 × 10 2×(10 22 − 1)/9 − 1 (that is, 1 followed by 2 222 222 222 222 222 222 222 nines). For any fixed base, the sum of the digits of a number is proportional to its logarithm ; therefore, the additive persistence is proportional to the iterated logarithm .
For divisibility by 9, this test is called the rule of nines and is the basis of the casting out nines technique for checking calculations. Digit sums are also a common ingredient in checksum algorithms to check the arithmetic operations of early computers. [ 3 ]
Casting out nines is a quick way of testing the calculations of sums, differences, products, and quotients of integers in decimal, a method known as long ago as the 12th century. [3] If an odd perfect number exists, it will have at least nine distinct prime factors. [4] Non-intersecting chords between four points on a circle
The smaller numbers, for use when subtracting, are the nines' complement of the larger numbers, which are used when adding. In mathematics and computing , the method of complements is a technique to encode a symmetric range of positive and negative integers in a way that they can use the same algorithm (or mechanism ) for addition throughout ...
The Archimedean property: any point x before the finish line lies between two of the points P n (inclusive).. It is possible to prove the equation 0.999... = 1 using just the mathematical tools of comparison and addition of (finite) decimal numbers, without any reference to more advanced topics such as series and limits.
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Rule of nines or rule of nine may refer to: Rule of nine (linguistics), an orthographic rule of the Ukrainian language. Rule of nines (mathematics), a test for divisibility by 9 involving summing the decimal digits of a number; Wallace rule of nines, used to determine the percentage of total body surface area affected when assessing burn injuries