slug: mathar-a174193-order-four-recurrence
bibkey: mathar2016a174193
doi: null
url: https://oeis.org/A174193
triage: theorem
motivation_gids:
  - D5/S1/Recurrence/Algebraic/MatharA174193OrderFourRecurrence.result

Mathar’s OEIS A174193 order-four recurrence

Problem

R. J. Mathar’s unnumbered FORMULA entry for OEIS A174193 gives the algebraic series [ \frac{1-8x+13x^2+24x^3-48x^4-(1-6x+x^2+34x^3-26x^4-4x^5)\sqrt{1-4x}}{2x^2(1-x)(1-4x)^2} ] and conjectures the displayed order-four recurrence for its coefficients. The formal statement uses rational power series, a branch $s$ with constant coefficient one and $s^2=1-4X$, and the cleared equation $DA=P-Bs$. It asserts existence of such a source series and the recurrence for every such series and every natural $n\ge 4$.

Statement echo

The Lean claim contains the existence conjunct, the universal source-series predicate, the guard $4\le n$, natural lagged indices $n-1$ through $n-4$, and the five rational polynomial coefficient terms exactly. IsSourceSeries contains $\exists s$, $s(0)=1$, $s^2=p$, and $DA=P-Bs$.

Motivation

The source still labels the recurrence a conjecture. The settling declaration is D5.S1.Recurrence.Algebraic.MatharA174193OrderFourRecurrence.result, preregistered in issue #24106. The identification of this algebraic series with the counting series of $\mathrm{Av}(321{)}^{+1}$ and the background paper’s Section 4 questions are separate claims.

Gap

The literature screen recorded in issue #24106 found no published settlement within its checked scope. The OEIS entry remains labelled “Conjecture”; the recurrence is absent from arXiv:2007.15111v1 and from the screened related sources. The screen is partial, and completeness is ASSUMED-UNVERIFIED.

Route

Map Mathlib’s Catalan series to rational coefficients and set $s=1-2XC$. The Catalan equation gives $s^2=1-4X$; polynomial normalization shows $P-Bs$ has a factor $X^2$, and a unit denominator constructs a source series. Differentiating $DA=P-Bs$ twice and clearing the nonzero factors gives an inhomogeneous second-order Euler identity with cubic right-hand side $H$. Two explicit polynomial certificates cancel the square-root terms. Since the coefficients of $H$ vanish above degree three, coefficient extraction at $n\ge 4$ gives the recurrence. The reused Euler-coefficient theorem is D5.S1.Recurrence.A308815DFiniteRecurrence.euler_coeff.

Falsifier

A source series satisfying the stated branch and cleared equation whose coefficient recurrence fails at some natural $n\ge 4$ would refute the claim. A failure of the permutation-counting identification would not refute this formal algebraic claim.

Evidence

The kernel-checked declaration is D5.S1.Recurrence.Algebraic.MatharA174193OrderFourRecurrence.result. Its axiom closure is contained in {propext, Classical.choice, Quot.sound}. The source note is Library/Words/mathar2016a174193.md.

The independent checker is in the-omega-institute/trureturing-experiments at commit b7f0518818771c2150a082e79fdfe6abffd8598e, path docs/reports/mathar-a174193/check.py; its SHA-256 is 38ed870ab06543b0ba8dffcac775a263b844902ff5fbd34f81c0432f1335bfbb. The command python3 docs/reports/mathar-a174193/check.py exits 0 and reports ALL_CHECKS_OK. It checks the two polynomial certificates, 30 displayed OEIS coefficients, 197 recurrence residuals for $4\le n\le 200$, hook-length values through 25, and deletion counts through 7.

Triage

• The exact algebraic source series exists, and every source series satisfies the stated recurrence for all $n\ge 4$. Proved by the kernel-checked result; the existence and universal clauses are both in claim.
• The source equation yields $LA=H$ with $H$ cubic; this is the cancellation mechanism that gives the order-four recurrence. Proved on the live path of result by the consumed inhomogeneous identity and the two polynomial certificates.
• The independent checker verifies both polynomial certificates, all 30 displayed OEIS coefficients, 197 recurrence residuals ($n=4,\dots ,200$), the hook-length values through 25, and deletion counts through 7. Computed by python3 docs/reports/mathar-a174193/check.py at the pinned experiment commit; exit 0 and the script SHA-256 above. These finite checks are corroboration.
• Identification of the source series with the counting series of $\mathrm{Av}(321{)}^{+1}$ is outside the claim and remains unproved here. Open; no declaration in this module states that identification.
• The background paper’s Section 4 injection and all-$t$ questions remain unproved here. Open; they are outside claim and have no declaration in this module.
• For every formal root $s$ with $s^2=p$, the cleared first and second derivative identities hold; root_derivatives requires only the square equation. Proved by the consumed root_derivatives declaration on the live path to inhomogeneous and result.
• A general theorem for other rational combinations of algebraic roots is not delivered; this proof establishes the fixed stated coefficients. Open; the module contains only the fixed A174193 coefficients.

What the settlement shows

The cancellation identities remove the normalized square-root component from a second-order Euler operator and leave a cubic forcing term. The result therefore settles the exact all-index recurrence for every formal source series satisfying the cleared algebraic equation, while leaving the permutation interpretation, Section 4 injection, all-$t$ questions and a general root-combination theorem open.

The escape audit is unfinished under issue #25507 for result and the published owner D5.S1.Recurrence.A308815DFiniteRecurrence.euler_coeff; no declared_validated registration is claimed without the required CI reading.

ASSUMED-UNVERIFIED

The literature screen is bounded and does not establish worldwide completeness, priority, or the absence of a later independent proof. The publisher version of the background article and several later citing works were not fully read. The escape-audit registrations remain unfinished until their typed evidence and required CI current DTR readings exist.