CollapseProblem 412Let σ1(n)=σ(n)\sigma_1(n)=\sigma(n)σ1(n)=σ(n), the sum of divisors function, and σk(n)=σ(σk−1(n))\sigma_k(n)=\sigma(\sigma_{k-1}(n))σk(n)=σ(σk−1(n)). Is it true that, for every m,n≥2m,n\geq 2m,n≥2, there exist some i,ji,ji,j such that σi(m)=σj(n)\sigma_i(m)=\sigma_j(n)σi(m)=σj(n)?Source: erdosproblems.com/412Number theoryIterated functionsWiki pageStatusOpenNo claim settles this problem.ReferencesEr79dErdős, P., Some unconventional problems in number theory. Acta Math. Acad. Sci. Hungar. (1979), 71-80.