Euler's totient function
Euler's totient function counts the positive integers up to a given integer n that are relatively prime to n.
Note: It works for n < 1014-1
This version uses only GGb scripting, but here is another version with JavaScript:
https://www.geogebra.org/m/sg2njyd5
Script I
n = 123456
Inp = InputBox(n)
SetCaption(Inp, "n = ")
facts = Factors(n)
phi = If(n <=0 , ?, If( n == 1, 1, Product(Sequence(Element(facts, i, 1)^(Element(facts, i, 2) - 1) (Element(facts, i, 1) - 1), i, 1, Length(facts))) )
text = "\phi(n) = " + phi
Script II
n = 123456
Inp = InputBox(n)
SetCaption(Inp, "n = ")
F = Unique(PrimeFactors(n))
phi = If(n<=0, ?, If(n == 1, 1, n Product(Zip(1 - 1 / p, p, F))))
text = "\phi(n) = " + phi
Script improved with the help of Thijs.