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  2. Modular arithmetic - Wikipedia

    en.wikipedia.org/wiki/Modular_arithmetic

    Adding 4 hours to 9 o'clock gives 1 o'clock, since 13 is congruent to 1 modulo 12. In mathematics, modular arithmetic is a system of arithmetic for integers, where numbers "wrap around" when reaching a certain value, called the modulus. The modern approach to modular arithmetic was developed by Carl Friedrich Gauss in his book Disquisitiones ...

  3. Modulo - Wikipedia

    en.wikipedia.org/wiki/Modulo

    Given two positive numbers a and n, a modulo n (often abbreviated as a mod n) is the remainder of the Euclidean division of a by n, where a is the dividend and n is the divisor. [ 1 ] For example, the expression "5 mod 2" evaluates to 1, because 5 divided by 2 has a quotient of 2 and a remainder of 1, while "9 mod 3" would evaluate to 0 ...

  4. Modulo (mathematics) - Wikipedia

    en.wikipedia.org/wiki/Modulo_(mathematics)

    Modulo is a mathematical jargon that was introduced into mathematics in the book Disquisitiones Arithmeticae by Carl Friedrich Gauss in 1801. [3] Given the integers a, b and n, the expression "a ≡ b (mod n)", pronounced "a is congruent to b modulo n", means that a − b is an integer multiple of n, or equivalently, a and b both share the same remainder when divided by n.

  5. Modulus (algebraic number theory) - Wikipedia

    en.wikipedia.org/wiki/Modulus_(algebraic_number...

    A modulus is a formal product [3] [4] where p runs over all places of K, finite or infinite, the exponents ν ( p) are zero except for finitely many p. If K is a number field, ν ( p ) = 0 or 1 for real places and ν ( p ) = 0 for complex places. If K is a function field, ν ( p ) = 0 for all infinite places. In the function field case, a ...

  6. Luhn algorithm - Wikipedia

    en.wikipedia.org/wiki/Luhn_algorithm

    Luhn algorithm. The Luhn algorithm or Luhn formula, also known as the " modulus 10" or "mod 10" algorithm, named after its creator, IBM scientist Hans Peter Luhn, is a simple check digit formula used to validate a variety of identification numbers. It is described in US patent 2950048A, granted on 23 August 1960. [1]

  7. Check digit - Wikipedia

    en.wikipedia.org/wiki/Check_digit

    The digit the farthest to the right (which is multiplied by 1) is the check digit, chosen to make the sum correct. It may need to have the value 10, which is represented as the letter X. For example, take the ISBN 0-201-53082-1: The sum of products is 0×10 + 2×9 + 0×8 + 1×7 + 5×6 + 3×5 + 0×4 + 8×3 + 2×2 + 1×1 = 99 ≡ 0 (mod 11). So ...

  8. Fermat's theorem on sums of two squares - Wikipedia

    en.wikipedia.org/wiki/Fermat's_theorem_on_sums_of...

    In additive number theory, Fermat 's theorem on sums of two squares states that an odd prime p can be expressed as: with x and y integers, if and only if. The prime numbers for which this is true are called Pythagorean primes. For example, the primes 5, 13, 17, 29, 37 and 41 are all congruent to 1 modulo 4, and they can be expressed as sums of ...

  9. Quadratic residue - Wikipedia

    en.wikipedia.org/wiki/Quadratic_residue

    0 2 ≡ 8 2 ≡ 16 2 ≡ 0 2 2 ≡ 6 2 ≡ 10 2 ≡ 14 2 ≡ 4 4 2 ≡ 12 2 ≡ 16. So a nonzero number is a residue mod 8, 16, etc., if and only if it is of the form 4 k (8n + 1). A number a relatively prime to an odd prime p is a residue modulo any power of p if and only if it is a residue modulo p. [8] If the modulus is p n, then p k a is a ...