Erdős Problem 825 #
Reference: erdosproblems.com/825
theorem
erdos_825.variants.necessary_cond
(C : ℝ)
(hC : 0 < C)
(h : ∀ (n : ℕ), ↑((ArithmeticFunction.sigma 1) n) > C * ↑n → ∃ s ⊆ n.properDivisors, n = s.sum id)
:
Show that if the constant $C > 0$ is such that every integer $n$ with $\sigma(n) > Cn$ is the distinct sum of proper divisors of $n$, then we must have $C > 2$.