online calculator for the totient function

(aka Euler’s phi function)
for example, φ(10) = 4, because 1, 3, 7, and 9 are relatively prime to 10
Here’s the link.
keywords:
[mathematics]
[relatively prime]
[coprime]
[relatively-prime]
[co-prime]
[prime factorization]
[multiplicative function]
[function-value lookups]
[function-evaluation]
[function evaluation]