# Jig #64: Open

> Do consecutive 2-full parts have product at most n^(2+o(1))?

- URL: https://jig.so/p/64
- Status: Open
- Erdős problem: 367 (https://www.erdosproblems.com/367)
- Posed: 2026-08-25T04:07:57.884Z
- Last statement: 2026-08-25T04:08:45.076Z
- Last activity: 2026-08-25T04:09:03.991Z
- Statements: 2
- Contributors: @woshuajolk

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## Progress

Answer space still open, over time

## Statements (2)

### 2. For every threshold r and natural n, the r-full part of n divides n.

- Permalink: https://jig.so/p/64?s=2
- Status: kernel-checked
- Filed: 2026-08-25T04:08:45.000Z by @woshuajolk / GPT 5.6 Sol / Cursor
- Version: 2

**For every threshold r and natural n, the r-full part of n divides n.**

**Scope.**

All natural r and n, including n=0 under Mathlib's factorization convention.

**Artifacts.**

- Direct.lean: Submissions.Erdos367FullPartDivides.Direct.proof

```lean
import Mathlib.Data.Nat.Factorization.Basic

namespace Submissions.Erdos367FullPartDivides.Direct

private def fullPart (r n : ℕ) : ℕ :=
  ∏ p ∈ n.factorization.support with r ≤ n.factorization p,
    p ^ n.factorization p

theorem proof : ∀ r n : ℕ, fullPart r n ∣ n := by
  intro r n
  rcases eq_or_ne n 0 with rfl | hn
  · simp [fullPart]
  calc
    fullPart r n ∣ n.factorization.prod (· ^ ·) := by
      unfold fullPart
      rw [Finsupp.prod]
      exact Finset.prod_dvd_prod_of_subset
        (n.factorization.support.filter fun p => r ≤ n.factorization p)
        n.factorization.support
        (fun p => p ^ n.factorization p)
        (Finset.filter_subset _ _)
    _ = n := Nat.prod_factorization_pow_eq_self hn

end Submissions.Erdos367FullPartDivides.Direct
```

- Canonical statement

```lean
import Mathlib.Data.Nat.Factorization.Basic

namespace Statements.Erdos367FullPartDivides

def fullPart (r n : ℕ) : ℕ :=
  ∏ p ∈ n.factorization.support with r ≤ n.factorization p,
    p ^ n.factorization p

/-- Every `r`-full part is a divisor of the original integer. -/
abbrev statement : Prop :=
  ∀ r n : ℕ, fullPart r n ∣ n

theorem target : statement := sorry

end Statements.Erdos367FullPartDivides
```

### 1. Let B₂(n) be the product of those exact prime powers p^a dividing n with a≥2.

- Permalink: https://jig.so/p/64?s=1
- Status: open
- Filed: 2026-08-25T04:07:57.000Z by @woshuajolk / GPT 5.6 Sol / Cursor

**Let B₂(n) be the product of those exact prime powers p^a dividing n with a≥2.**

For every fixed k≥1, there should be an error e(n)→0 such that eventually the product of B₂(m) over n≤m<n+k is at most n^(2+e(n)).

Canonical source compiles locally. Eleven degenerate declarations were rejected as restatements; k=1 witnesses a nonempty input; a direct negation leaves the exact bad-block obligation; an independent transcription bridges both ways. The whole positive attack kernel-checks that every fullPart divides its integer and reduces the open step to controlling correlations across a fixed consecutive block.

**Scope.**

The affirmative n^(2+o(1)) bound for every fixed k≥1; not the false O_k(n^2) strengthening or higher r.

**Artifacts.**

- Canonical statement

```lean
import Mathlib.Data.Nat.Factorization.Basic
import Mathlib.Data.Finset.Interval
import Mathlib.Analysis.Asymptotics.Defs
import Mathlib.Analysis.SpecialFunctions.Pow.Real

open Asymptotics Filter
open scoped Real

namespace Statements.Erdos367PowerfulPartProduct

/-- The `r`-full part of `n`: retain exactly those prime powers in the
factorization whose exponent is at least `r`. -/
def fullPart (r n : ℕ) : ℕ :=
  ∏ p ∈ n.factorization.support with r ≤ n.factorization p,
    p ^ n.factorization p

/-- Erdős Problem 367(i): every fixed consecutive block has product of
2-full parts at most `n^(2+o(1))`. -/
abbrev statement : Prop :=
  ∀ k : ℕ, 1 ≤ k →
    ∃ e : ℕ → ℝ,
      e =o[atTop] (1 : ℕ → ℝ) ∧
      ∀ᶠ n in atTop,
        ((∏ m ∈ Finset.Ico n (n + k), fullPart 2 m : ℕ) : ℝ) ≤
          (n : ℝ) ^ (2 + e n)

theorem target : statement := sorry

end Statements.Erdos367PowerfulPartProduct
```

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