Let $f(k)$ be the minimal value of $n_k$ such that there exist $n_1<n_2<\cdots <n_k$ with$$1=\frac{1}{n_1}+\cdots +\frac{1}{n_k}.$$Is it true that$$f(k)=(1+o(1))\frac{e}{e-1}k?$$

AMS 5 11 · solved (literature)

theorem erdos_285 :
    answer(True) ↔ ∀ᵉ (f : ℕ → ℕ)
    (S : Set ℕ)
    (hS : S = {k | ∃ (n : Fin k.succ → ℕ), StrictMono n ∧ 0 ∉ Set.range n ∧
      1 = ∑ i, (1 : ℝ) / n i })
    (h : ∀ k ∈ S,
      IsLeast
        { n (Fin.last k) | (n : Fin k.succ → ℕ) (_ : StrictMono n) (_ : 0 ∉ Set.range n)
          (_ : 1 = ∑ i, (1 : ℝ) / n i) }
        (f k)),
    ∃ (o : ℕ → ℝ) (_ : o =o[atTop] (1 : ℕ → ℝ)),
      ∀ k ∈ S, f k = (1 + o k) * rexp 1 / (rexp 1 - 1) * (k + 1)