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An example of a non-multiplicative function is the arithmetic function r 2 (n) - the number of representations of n as a sum of squares of two integers, positive, negative, or zero, where in counting the number of ways, reversal of order is allowed. For example:
For example, if a function f is multiplicative then it is completely multiplicative if and only if its Dirichlet inverse is where is the Möbius function. [2] Completely multiplicative functions also satisfy a distributive law. If f is completely multiplicative then
As another example, φ(1) = 1 since for n = 1 the only integer in the range from 1 to n is 1 itself, and gcd(1, 1) = 1. Euler's totient function is a multiplicative function, meaning that if two numbers m and n are relatively prime, then φ(mn) = φ(m)φ(n).
[note 3] For example, multiplication of integers is a function of two variables, or bivariate function, whose domain is the set of all ordered pairs (2-tuples) of integers, and whose codomain is the set of integers. The same is true for every binary operation.
The Möbius function () is a multiplicative function in number theory introduced by the German mathematician August Ferdinand Möbius (also transliterated Moebius) in 1832. [ i ] [ ii ] [ 2 ] It is ubiquitous in elementary and analytic number theory and most often appears as part of its namesake the Möbius inversion formula .
The following is a table of the Bell series of well-known arithmetic functions. The Möbius function has () =.; The Mobius function squared has () = +.; Euler's totient has () =.; The multiplicative identity of the Dirichlet convolution has () =
In number theory, the Legendre symbol is a multiplicative function with values 1, −1, 0 that is a quadratic character modulo of an odd prime number p: its value at a (nonzero) quadratic residue mod p is 1 and at a non-quadratic residue (non-residue) is −1. Its value at zero is 0.
These properties concern how the function is affected by arithmetic operations on its argument. The following are special examples of a homomorphism on a binary operation: Additive function: preserves the addition operation: f (x + y) = f (x) + f (y). Multiplicative function: preserves the multiplication operation: f (xy) = f (x)f (y).