[A] $2535$.
[B] $2847$.
[C] $2769$.
[D] $2028$.
Solução
Os divisores de $n$ serão: $$D(n)=\{1, 3, 13, \cdots , \dfrac{n}{13}, \dfrac{n}{3}, n\}$$ Sendo assim: $$\dfrac{n}{13}+\dfrac{n}{3}+n=3905$$ $$\dfrac{3n}{39}+\dfrac{13n}{39}+\dfrac{39n}{39}=3905$$ $$\dfrac{55n}{39}=3905$$ $$55n=152295$$ $$n=2769$$
Resposta: Item C