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Verhoeff had the goal of finding a decimal code—one where the check digit is a single decimal digit—which detected all single-digit errors and all transpositions of adjacent digits. At the time, supposed proofs of the nonexistence [6] of these codes made base-11 codes popular, for example in the ISBN check digit.
The final character of a ten-digit International Standard Book Number is a check digit computed so that multiplying each digit by its position in the number (counting from the right) and taking the sum of these products modulo 11 is 0. The digit the farthest to the right (which is multiplied by 1) is the check digit, chosen to make the sum correct.
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.
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).
Sixth rightmost digit = 1 × −2 = −2 Seventh rightmost digit = 6 × 1 = 6 Eighth rightmost digit = 3 × 3 = 9 Ninth rightmost digit = 0 Tenth rightmost digit = 1 × −1 = −1 Sum = 33 33 modulus 7 = 5 Remainder = 5 Digit pair method of divisibility by 7. This method uses 1, −3, 2 pattern on the digit pairs. That is, the divisibility 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.
Let be a natural number which can be written in base as the k-digit number ... where each digit is between and inclusive, and = =.We define the function : as () = =. (As 0 0 is usually undefined, there are typically two conventions used, one where it is taken to be equal to one, and another where it is taken to be equal to zero.
The digit at position b – 1 must be at least 1, meaning that there is at least one instance of the digit b – 1 in m. At whatever position x that digit b – 1 falls, there must be at least b – 1 instances of digit x in m. Therefore, we have at least one instance of the digit 1, and b – 1 instances of x. If x > 1, then m has more than b ...