Which of the following is true for the Euler's totient function ϕ(n)\phi(n)ϕ(n)?
ϕ(p)=p\phi(p) = pϕ(p)=p for prime ppp
ϕ(mn)=ϕ(m)ϕ(n)\phi(mn) = \phi(m)\phi(n)ϕ(mn)=ϕ(m)ϕ(n) if gcd(m,n)>1\gcd(m, n) > 1gcd(m,n)>1
ϕ(pk)=pk−pk−1\phi(p^k) = p^k - p^{k-1}ϕ(pk)=pk−pk−1
ϕ(n)\phi(n)ϕ(n) is always odd for n>2n > 2n>2