slug: oeis-a382124-hanna-sigma-exponential-mod-three
bibkey: hanna2025a382124a382125
doi: null
url: https://oeis.org/A382124
triage: theorem
motivation_gids:
  - D5/S3/Arith/Robin/HannaSigmaProductExpModThree.result

Hanna’s A382124 congruence

Problem

OEIS A382124 states: “Conjecture: a(n) == A382125(3*n) (mod 3) for n >= 0.”

Write $A(x)=\exp ({\sum }_{n\ge 1}\sigma (n)\sigma (2n)x^n/(3n))$ and $B(x)=\exp ({\sum }_{n\ge 1}\sigma (n)\sigma (2n)x^n/n)$, with $\sigma (n)={\sum }_{d\mid n}d$. The public rational-series definitions are exactly the preregistered expressions.

Statement echo

Motivation

The named conjecture is preregistered in #18863. The exact rational formal series carry integer witnesses for the source’s congruence statements. Its settling declaration is D5/S3/Arith/Robin/HannaSigmaProductExpModThree.result.

Gap

The literature screen in #18863 and #18864 covers the OEIS entries and their links, the OEIS Open benchmark and four OEIS-proof papers, arXiv:2610.15849, arXiv:2410.07237, arXiv:2608.11941 and arXiv:2607.24832. No settlement was found in that searched scope. Completeness is ASSUMED-UNVERIFIED.

Route

Put $c(n)=\sigma (n)\sigma (2n)/3$. The arithmetic argument proves that $c$ is integer valued and satisfies the Dold congruences. For the prime three, writing $m=3^{a}k$ with $3\nmid k$ gives $c(3^{a}k)=\sigma (3^a{)}^{2}c(k)$, and $\sigma (3^{a+1})-\sigma (3^a)=3^{a+1}$. This supplies the required power of three. The other primes use the Dold congruences of the divisor sum and their product and index-scaling closure.

The shared DoldExponentialIntegrality.integral_exp_of_dold theorem proves the sufficient Dold integrality criterion. HannaSigmaProductExpModThree.AIntegral applies it to $c$. The identity integerCube_map identifies the cube of the integral lift of $A$ with $B$. The theorem cube_residues applies characteristic-three Frobenius to that lift.

Falsifier

A nonintegral coefficient of $A$, or an index violating a source congruence, contradicts the formal settlement under the displayed definitions. The finite experiment below is supporting evidence; the universal result is the Lean theorem.

Evidence

The settling theorem is D5/S3/Arith/Robin/HannaSigmaProductExpModThree.result. The axiom closure of every public declaration is contained in {propext, Classical.choice, Quot.sound}. The full statement appears in its Blueprint theorem node.

The supporting source is adapted from AINTLIB at commit 1e63feb21e2dd9e54908d14c9c07058eff3ff1d4, with attribution and Apache-2.0 license in Library/RecurrenceComposition/aintlib2026dieudonnedwork.md.

The escape audit is unfinished: #19891. The published owner declarations D5.S3.Arith.Robin.PrimeFiberPropagation.sigma_prime_pow_succ, D5.S1.Recurrence.LinearRows.LinearExponentDyadicSupport.Agree, D5.S1.Recurrence.LinearRows.LinearExponentDyadicSupport.pow_change and D5.S1.Recurrence.Residue.ParametricExponentialSquareCongruence.linear_ode_unique are included in that unfinished audit. No delivered Reg registration is classified as declared_validated.

Experiment

Pinned experiment directory. Run python3 check.py 300 in that directory; exit 0, RESULT PASS. The script SHA-256 is 319ee58b884641c875833eb3e830906af72d593ab73e1d6b0da6ff155cd352f3.

Computed scope: $c(n)$ is integral for $1\le n\le 900$; the Dold congruences hold for primes $p<40$ and $pm\le 900$; $A$ is integral through degree 300 and $B$ through degree 900; their tested coefficients match the b-files; $B=A^3$ through degree 300; $a(n)\equiv b(3n)(\mathrm{mod}3)$ for $0\le n\le 300$; and $b(3n+1)\equiv b(3n+2)\equiv 0(\mathrm{mod}3)$ for $0\le n<300$.

Declaration classification

Names in this table are relative to D5.S3.Arith.Robin.HannaSigmaProductExpModThree. The shared live escape witness is D5.S1.Recurrence.Algebraic.DoldExponentialIntegrality.IsRIntegralPS.dieudonneDwork_mpr; content classification expands the same-delivery support.

Triage

What the settlement shows

• Proved in Lean — mechanism and integrality. DoldExponentialIntegrality.integral_exp_of_dold proves integrality for every integer ghost sequence satisfying Dold. HannaSigmaProductExpModThree.AIntegral establishes the integrality of $A$; the arithmetic factorization at three closes the denominator-prime case.
• Proved in Lean — exact scope. HannaSigmaProductExpModThree.result and HannaSigmaProductExpModThreeCube.result prove the two complete preregistered claims at every natural index. They use no coefficient cutoff.
• Proved in Lean — reusable structure. The general sufficient Dold criterion has an arbitrary integer ghost sequence. CubicFifteenSubstitutionParity.prime_power_subst supplies Frobenius for arbitrary series over a prime residue field. No further named conjecture is claimed settled.
• Computed — owner integration. The source inventory publishes LinearExponentDyadicSupport.pow_change and ParametricExponentialSquareCongruence.linear_ode_unique, with complete Scribe nodes. CubicFifteenSubstitutionParity.prime_power_subst is already public on the protected base. These are reused through their owners.
• Computed — shared support. The delivered source inventory has one shared DoldExponentialIntegrality module, consumed by HannaSigmaProductExpModThree.AIntegral; no second copy is delivered. Open: integration of the independent fibpow lane is outside this delivery.
• Computed — publication structure. Each of the two named problems has its own dossier and one OpenProblemResolutionClaim on its settling result. Open: four-slot registration evidence is incomplete under #19891; required CI and the review triplet govern admission.
• Computed — coefficient checks. The experiment entry gives the command, script identity and exact finite ranges. Those ranges carry no uniform numerical conclusion.
• Open. The residues of $A$ itself modulo three are not determined here.

Inventory evidence: git grep -n -E "^(private )?(noncomputable )?(def|theorem) (pow_change|linear_ode_unique|prime_power_subst|integral_exp_of_dold)|OpenProblemResolutionClaim" -- D5/S1/Recurrence D5/S3/Arith/Robin Blueprint/D5/S1/Recurrence Blueprint/D5/S3/Arith/Robin (exit 0). The module and Scribe inventories establish the publication and sharing statements; they are not mathematical proofs.

Generalization proved in prose

Let $q$ be prime and let $f:\mathbb{N}\to \mathbb{Z}$ satisfy the Dold congruences. Suppose $q\mid f(n)$ for every $n$ and $q^{v_q(m)+2}\mid f(qm)-f(m)$ for every positive $m$. Put $g(n)=f(n)/q$. At primes $p\ne q$, cancellation of the factor $q$ preserves the required $p$-power divisibility. At $p=q$, the extra power of $q$ gives $q^{v_q(m)+1}\mid g(qm)-g(m)$. Thus $g$ satisfies Dold, and the sufficient criterion makes $\exp ({\sum }_{n\ge 1}g(n)x^n/n)$ integral. Reduction modulo $q$ and Frobenius identify its $q$-th power with substitution of $x^q$. This is a prose consequence of the general criterion, not a new Lean declaration or another named settlement.

The source’s assertion that $B$ is the self-convolution cube of $A$ is represented by integerCube_map after rational mapping. The two stated residue conjectures follow. No other source result is asserted to depend on them.

ASSUMED-UNVERIFIED

Literature completeness, priority, the source’s identification with the formal generating functions and the fidelity of the prose-to-Lean correspondence are outside the kernel. The source and literature readings are attributed to the preregistration’s orchestrator and literature seat. The experiment is finite. The escape-registration evidence remains incomplete under #19891.