In number theory, the radical of a positive integer n is defined as the product of the distinct prime numbers dividing n. Each prime factor of n occurs exactly once as a factor of this product:
The radical plays a central role in the statement of the abc conjecture.[1]
Radical numbers for the first few positive integers are
For example,
and therefore
The function is multiplicative (but not completely multiplicative).
The radical of any integer is the largest square-free divisor of and so also described as the square-free kernel of .[2] There is no known polynomial-time algorithm for computing the square-free part of an integer.[3]
The definition is generalized to the largest -free divisor of , , which are multiplicative functions which act on prime powers as
The cases and are tabulated in OEIS: A007948 and OEIS: A058035.
The notion of the radical occurs in the abc conjecture, which states that, for any , there exists a finite such that, for all triples of coprime positive integers , , and satisfying ,[1]
For any integer , the nilpotent elements of the finite ring are all of the multiples of .
The Dirichlet series is