$n' = n$

What is the sum of the first two positive integers which satisfy $n' = n$ , where $n'$ is the arithmetic derivative of $n$ ?

Clarification: The arithmetic derivative of $n$ is given by:

• $n' = 0$ for $n$ = 1 or 0.
• $n' = 1$ if is prime.
• $n' = a'b + b'a$ if $n$ is composite, where $a$ and $b$ are factors of $n$