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@Marygold-Dusk Marygold-Dusk commented Nov 20, 2025

This is the statement of Erdős Conjecture 386.

fixes #703

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Thanks for the contribution! Here are some comments :)

def erdos_386_equation (a b : ℕ) (A : Finset ℕ) :=
Nat.choose a b = ∏ α ∈ A, α

/-
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Suggested change
/-
/--

Docstrings (i.e. comments over theorems / definitions) must start like this.

Comment on lines 32 to 33
def erdos_386_equation (a b : ℕ) (A : Finset ℕ) :=
Nat.choose a b = ∏ α ∈ A, α
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Since this is only used once in the statement of erdos_386 I would not add it as a definition, and rather just state it there.

Comment on lines 36 to 39
The following set contains all solutions `(n, k, P)` to the Erdős problem 386.
A solution is a tuple `(n, k, P)`, where `n ≥ 2` and `k` are an integers and `P`
is a non-empty finite set of
distinct prime numbers, such that it's product is binomial coefficient n choose k.
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Could you make this comment more precise? For example you do not mention that 2 ≤ k ≤ n - 2 and that the elements of P need to be primes.

Comment on lines 41 to 47
def erdos_386_solutions : Set (ℕ × ℕ × Finset ℕ) := {
(n, k, P) |
(n ≥ 2 ∧ 2 ≤ k ∧ k ≤ n - 2) ∧
P.Nonempty ∧
(∀ p ∈ P, p.Prime) ∧
erdos_386_equation n k P
}
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I think this is missing the condition that the primes are consecutive.

-/
def erdos_386_solutions : Set (ℕ × ℕ × Finset ℕ) := {
(n, k, P) |
(n ≥ 2 ∧ 2 ≤ k ∧ k ≤ n - 2) ∧
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Suggested change
(n ≥ 22 ≤ k ∧ k ≤ n - 2) ∧
(n ≥ 22 ≤ k ∧ k ≤ n - 2) ∧

I would put either n ≥ 4 or no condition on n here, since for n < 3 no such k exist.

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Erdős Problem 386

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