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erdos_888

Specification

What is the size of the largest subset `A` of `{1,...,n}` such that if `a ≤ b ≤ c ≤ d ∈ A` and `abcd` square then `ad=bc`

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Lean 4 Statement 
theorem erdos_888 : ∀ n, Nat.findGreatest (p n) n = (answer(sorry) : ℕ → ℕ) n
ID: ErdosProblems__888__erdos_888
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