slug: mathar-2012-a108958-recurrence
bibkey: mathar2012a108958
doi: null
url: https://oeis.org/A108958
triage: theorem
motivation_gids:
  - D5/S3/Combinatorics/ZeroQuantumPairsRecurrence.result

Mathar’s recurrence for the zero-quantum transition pairs A108958

Problem

OEIS A108958 counts the unordered pairs of distinct binary words of length n with the same number of 1’s, a(n) = Σ_{k=0}^{n} C(C(n,k), 2); for n spins 1/2 these are the nontrivial zero-quantum transitions. Its formula field records:

Conjecture: n*(n-2)a(n) +2(-3n^2+7n-3)a(n-1) +4(n-1)(2n-3) *a(n-2)=0. - R. J. Mathar, Apr 04 2012

Issue #10598 fixes the reading: a is defined by the entry’s first formula line (also at n = 0, value 0), and the recurrence is asserted for every n ≥ 2.

Motivation

The entry still marks the recurrence as a conjecture (revision 77, 2025-11-05). D5/S3/Combinatorics/ZeroQuantumPairsRecurrence.result proves it for every n ≥ 2.

Gap

Issue #10598 preregisters the proof route and the literature check. The entry gives the closed form binomial(2n−1, n−1) − 2^(n−1) (Jovovic, 2005) but no proof of the recurrence; the repository has no declaration about A108958. not-found-in-searched-scope.

Route

1. 2 a(n) = Σ_k C(n,k)^2 − Σ_k C(n,k) = C(2n, n) − 2^n.
2. u(n) = C(2n, n) satisfies n u(n) = 2(2n − 1) u(n − 1), which makes the three-term recurrence for u an identity in u(n − 1).
3. w(n) = 2^n satisfies the recurrence identically, and the recurrence is linear, so a = (u − w)/2 satisfies it.

Falsifier

The proof would fail if the closed form of step 1 or the identities of steps 2 and 3 failed for some n ≥ 2.

Evidence

Exact integer computation: the recurrence holds for n = 2, …, 299 and 2 a(n) = C(2n, n) − 2^n for n = 0, …, 199 (issue #10598).

The canonical source is D5/S3/Combinatorics/ZeroQuantumPairsRecurrence.lean. Its public declarations are a, claim, and result. The frozen module state has statement identity sha256:927b7ebb2138f5fbeb71a382fe8b6aa929e43e643e921f62891077b6f983bc13. The result declaration has statement identity sha256:a40591f2537a002a1a0b9eec820b55ae6b03587e44c472b212532221be2ca8ec. The Freeze event is sha256:536825db74874f9d1e59f65a453748cddc2d8d8441b75ef0a2ca324a6786268a. It has no project-level frozen prerequisite. The proof uses only the standard axioms propext, Classical.choice and Quot.sound; no sorry, native_decide, or new axiom.

Triage

Tier 1 external named conjecture (OEIS formula field), preregistered in issue #10598 before the probe. theorem; resolution proved. The public theorem has proof_shape: bind-only: every atomic fact is an instance of a pinned Mathlib lemma (the Vandermonde sum of squares, the binomial sum and the central binomial recurrence), combined by sum distribution and linear arithmetic. The settlement of the named conjecture is the new content, so the admission basis is open-problem-resolution; utility none.

ASSUMED-UNVERIFIED

The bounded literature check does not establish exhaustive worldwide novelty, priority, or the absence of an independent proof.