Additive function


In number theory, an additive function is an arithmetic function f of the positive integer n such that whenever a and b are coprime, the function of the product is the sum of the functions:

Completely additive

An additive function f is said to be completely additive if f = f + f holds for all positive integers a and b, even when they are not coprime. Totally additive is also used in this sense by analogy with totally multiplicative functions. If f is a completely additive function then f = 0.
Every completely additive function is additive, but not vice versa.

Examples

Example of arithmetic functions which are completely additive are:
Example of arithmetic functions which are additive but not completely additive are:
From any additive function f it is easy to create a related multiplicative function g i.e. with the property that whenever a and b are coprime we have:
One such example is g = 2f.

Summatory functions

Given an additive function, let its summatory function be defined by. The average of is given exactly as
The summatory functions over can be expanded as where
The average of the function is also expressed by these functions as
There is always an absolute constant such that for all natural numbers,
Let
Suppose that is an additive function with
such that as,
Then where is the Gaussian distribution function
Examples of this result related to the prime omega function and the numbers of prime divisors of shifted primes include the following for fixed where the relations hold for :