If $n > 0$ is an even composite integer, then $\varphi(n)$ is even?
17277
Why is Euler's Totient function always even?
34803
Evaluating even binomial coefficients
47211
Does $\varphi(x)\le\int_0^x\varphi(t)dt$ for all $x\in[0,\infty)$ imply $\varphi\equiv0$.
123117
Is it possible to find $n-1$ consecutive composite integers
90537
Converse of Fermat's Little Theorem.
151111
How do I show that $\frac{n}{\varphi(n)}=\sum\limits_{d \mid n} \frac{\mu^2(d)}{\varphi(d)}$?
120629
Prove if $n$ has a primitive root, then it has exactly $\phi(\phi(n))$ of them
72054
Show that $\deg f$ is even when $n$ is odd.
84010
Combinatorial proof that $\sum \limits_{k=0}^n \binom{2k}{k} \binom{2n-2k}{n-k} (-1)^k = 2^n \binom{n}{n/2}$ when $n$ is even
147517
Any group of order $n$ satisfying $\gcd (n, \varphi(n)) =1$ is cyclic
2900
How many $3$-subsets of $\{1,2,\ldots,10\}$ contain at least one even and one odd integer?
35712
Solve for n: $\varphi(2n)=\varphi(3n)$
53525
Infiniteness of non-twin primes.
35553
If $n$ is composite, so is $2^n-1$
106380
What is $n!$ when $n=0$?
128834
Proving the number of even and odd permutations of a subgroup $H<S_{n}$ are equal, provided $H$ is not contained in $A_{n}$
43764
Prove $P_m X P_n$ is Hamiltonian if and only if at least one of $m,n$ is even