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The check digit is computed as follows: Drop the check digit from the number (if it's already present). This leaves the payload. Start with the payload digits. Moving from right to left, double every second digit, starting from the last digit. If doubling a digit results in a value > 9, subtract 9 from it (or sum its digits).
For instance, the UPC-A barcode for a box of tissues is "036000241457". The last digit is the check digit "7", and if the other numbers are correct then the check digit calculation must produce 7. Add the odd number digits: 0+6+0+2+1+5 = 14. Multiply the result by 3: 14 × 3 = 42. Add the even number digits: 3+0+0+4+4 = 11.
The validity of a digit sequence containing a check digit is defined over a quasigroup. A quasigroup table ready for use can be taken from Damm's dissertation (pages 98, 106, 111). [3] It is useful if each main diagonal entry is 0, [1] because it simplifies the check digit calculation.
This is an accepted version of this page This is the latest accepted revision, reviewed on 17 January 2025. Observation that in many real-life datasets, the leading digit is likely to be small For the unrelated adage, see Benford's law of controversy. The distribution of first digits, according to Benford's law. Each bar represents a digit, and the height of the bar is the percentage of ...
There are only 21853 pseudoprimes base 2 that are less than 2.5 × 10 10 (see page 1005 of [3]). This means that, for n up to 2.5 × 10 10, if 2 n −1 (modulo n) equals 1, then n is prime, unless n is one of these 21853 pseudoprimes. Some composite numbers (Carmichael numbers) have the property that a n − 1 is 1 (modulo n) for every a that ...
the use of 2 to check whether a number is even or odd, as in isEven = (x % 2 == 0), where % is the modulo operator; the use of simple arithmetic constants, e.g., in expressions such as circumference = 2 * Math.PI * radius, [1] or for calculating the discriminant of a quadratic equation as d = b^2 − 4*a*c
If you look at a bank-issued check, you’ll see a series of numbers printed along the bottom edge of the check. The first set of numbers is the nine-digit bank routing number. The second set of ...
In number theory, a narcissistic number [1] [2] (also known as a pluperfect digital invariant (PPDI), [3] an Armstrong number [4] (after Michael F. Armstrong) [5] or a plus perfect number) [6] in a given number base is a number that is the sum of its own digits each raised to the power of the number of digits.