Python/maths/liouville_lambda.py

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"""
== Liouville Lambda Function ==
The Liouville Lambda function, denoted by λ(n)
and λ(n) is 1 if n is the product of an even number of prime numbers,
and -1 if it is the product of an odd number of primes.
https://en.wikipedia.org/wiki/Liouville_function
"""
# Author : Akshay Dubey (https://github.com/itsAkshayDubey)
from maths.prime_factors import prime_factors
def liouville_lambda(number: int) -> int:
"""
This functions takes an integer number as input.
returns 1 if n has even number of prime factors and -1 otherwise.
>>> liouville_lambda(10)
1
>>> liouville_lambda(11)
-1
>>> liouville_lambda(0)
Traceback (most recent call last):
...
ValueError: Input must be a positive integer
>>> liouville_lambda(-1)
Traceback (most recent call last):
...
ValueError: Input must be a positive integer
>>> liouville_lambda(11.0)
Traceback (most recent call last):
...
TypeError: Input value of [number=11.0] must be an integer
"""
if not isinstance(number, int):
raise TypeError(f"Input value of [number={number}] must be an integer")
if number < 1:
raise ValueError("Input must be a positive integer")
return -1 if len(prime_factors(number)) % 2 else 1
if __name__ == "__main__":
import doctest
doctest.testmod()