Erdős Problem #412

declared status 'open'. Formalized: yes. Let $\sigma_1(n)=\sigma(n)$, the sum of divisors function, and $\sigma_k(n)=\sigma(\sigma_{k-1}(n))$. Is it true that, for every $m,n\geq 2$, there exist some $i,j$ such that $\sigma_i(m)=\sigma_j(n)$? Prize: no. OEIS: A007497, A051572. Tags: iterated functions, number theory.

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