## Discrete Mathematics and Its Applications, Seventh Edition

To find the values of the Euler phi-function, we multiply the integers smaller than the number which are relatively prime to it. a) $ϕ(4)=3$ b) $ϕ(10)=ϕ(2⋅5)=3⋅7⋅9=189$ c) $ϕ(13)=12!=479001600$