Liouville function

In number theory, the Liouville function, named after French mathematician Joseph Liouville and denoted ${\displaystyle \lambda (n)}$, is an important arithmetic function. Its value is ${\displaystyle 1}$ if ${\displaystyle n}$ is the product of an even number of prime numbers, and ${\displaystyle -1}$ if it is the product of an odd number of prime numbers.