**Hint:** try to check [this online book] under this title **The math encyclopedia of smarandach type notion** in number theory include also arithmitic function , And bellow papers , However they include iterate sum of divisor function, but you w'ill find solution of your problem , papers include " meta perfect number:" **Cohen, Graeme L., and Herman JJ te Riele. "Iterating the sum-of-divisors function."** **Kátai, I. "On the prime power divisors of the iterates of $\phi(n)$ and $\sigma(n)$, Šiauliai** **Math." Semin 4.12 (2009): 125-143** **Experimental Mathematics 5.2 (1996): 91-100**. [this online book]:https://books.google.dz/books?id=DYEXAgAAQBAJ&pg=PA6&lpg=PA6&dq=best+books+for+sum+divisor+function&source=bl&ots=stuyvM_P2l&sig=ahjZEIrNT4ICHHsw4zGjEveMZZY&hl=fr&sa=X&ved=0ahUKEwicid3or9LYAhWIshQKHQo7CXw4ChDoAQhIMAM#v=onepage&q=best%20books%20for%20sum%20divisor%20function&f=false