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Time-keeping on this clock uses arithmetic modulo 12. 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.
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.
For a given positive integer , two integers and are called congruent modulo , written a ≡ b ( mod n ) {\displaystyle a\equiv b{\pmod {n}}} if a − b {\displaystyle a-b} is divisible by n {\displaystyle n} (or equivalently if a {\displaystyle a} and b {\displaystyle b} have the same remainder when divided by n {\displaystyle n} ).
Equivalently, the elements of this group can be thought of as the congruence classes, also known as residues modulo n, that are coprime to n. Hence another name is the group of primitive residue classes modulo n. In the theory of rings, a branch of abstract algebra, it is described as the group of units of the ring of integers modulo n.
In modular arithmetic, a number g is a primitive root modulo n if every number a coprime to n is congruent to a power of g modulo n. That is, g is a primitive root modulo n if for every integer a coprime to n, there is some integer k for which g k ≡ a (mod n). Such a value k is called the index or discrete logarithm of a to the base g modulo n.
gcd(r, n) = 1 for each r in R, R contains φ(n) elements, no two elements of R are congruent modulo n. [1] [2] Here φ denotes Euler's totient function. A reduced residue system modulo n can be formed from a complete residue system modulo n by removing all integers not relatively prime to n. For example, a complete residue system modulo 12 is ...
The particular case a = 1 (i.e., concerning the primes that are congruent to 1 modulo some n) can be proven by analyzing the splitting behavior of primes in cyclotomic extensions, without making use of calculus (Neukirch 1999, §VII.6).
It follows from this fact that all nonzero remainders modulo the square of which isn't congruent to can be grouped into unordered pairs (,) according to the rule that the product of the members of each pair is congruent to modulo (since by this fact for every we can find such an , uniquely, and vice versa, and they will differ from each other ...