MöbiusMu
The Möbius function.
Syntax

MöbiusMu(n)

n
is a positive integer

Description
If n
is a positive integer, then
⎧ +1 if n is squarefree and has an even number of prime factors MöbiusMu(n) = ⎨ −1 if n is squarefree and has an odd number of prime factors ⎩ 0 if n is not squarefree.
Examples
MöbiusMu(219557911565161)
−1
SequenceVector(25) @ MöbiusMu
(1, −1, −1, 0, −1, 1, −1, 0, 0, 1, −1, 0, −1, 1, 1, 0, −1, 0, −1, 0, 1, 1, −1, 0, 0)
∑(SequenceVector(100000) @ MöbiusMu)
−48
∑(SequenceVector(100000) @ MöbiusMu @ abs)
60794
n ≔ 12345; ∑(divisors(n) @ MöbiusMu)
0