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use crate::prime_factorize_trial_division::prime_factorize;
// TODO: use faster factorization algorithm.
pub fn mobius_function(n: u64) -> i8 {
assert!(n > 0);
if n == 1 {
return 1;
}
let mut u = 1;
for (_, e) in prime_factorize(n) {
if e > 1 {
return 0;
}
u *= -1;
}
u
}
#[cfg(test)]
mod tests {
#[test]
fn test() {
use super::*;
assert_eq!(mobius_function(1), 1);
assert_eq!(mobius_function(2), -1);
assert_eq!(mobius_function(4), 0);
}
}