  The Euler's totient function $ \varphi(n) $ counts the positive integers up
to a given integer $ n$ that are relatively prime to $ n $. We solve a problem
due to Lehmer that there is no composite number $ n $ such that $
\varphi(n)\mid n-1 $. We also note that there are infinitely many primes that
are not Sophie Germain primes.
