totient
Euler’s totient (phi) function.
Syntax

totient(n)

n
is an integer

Description
If n
is a positive integer, then totient(n)
is the number of positive integers less than or equal to n
that are relatively prime to n
.
Notes
If you use the totient
function frequently, you may want to assign it to the φ
symbol:
φ ≔ totient
Examples
totient(19871226)
6200064
φ ≔ totient; n ≔ 123456; ∑(divisors(n) @ φ)
123456