Metadata

slug: oeis-a379764-hanna-theta-mod-four
bibkey: hanna2026a379764
doi: null
url: https://oeis.org/A379764
triage: theorem
motivation_gids:
  - D5/S1/Recurrence/Bilateral/HannaThetaFourModFour.result

Hanna’s A379764 theta-four coefficient conjectures

Problem

Paul D. Hanna’s OEIS A379764 states:

G.f. A(x) satisfies Sum_{n=-oo..+oo} (4^nA(x)^n - 4A(x))^(n+1) = 2theta_4(x) = 2Sum_{n=-oo..+oo} (-x)^(n^2).

Conjecture: for n > 0, a(n) is odd iff n is a square.

Conjecture: for n > 0, a(n) == (-1)^(n-1) (mod 4) iff n is a square, otherwise a(n) is divisible by 4 if n is nonsquare.

The statement source and binding formal conventions are in #18830. The normalization is $A (0) = 0$ and $a (1) = 1$ . Integer powers of the summand are taken in rational Laurent series. The bilateral equation means equality at coefficient $N$ for every symmetric window $[- K, K]$ with $N + 1 \leq K$ ; no analytic convergence assertion is made.

Statement echo

All names below belong to D5.S1.Recurrence.Bilateral.HannaThetaFourModFour.

Source or binding convention	Lean counterpart	Fidelity
The sum defining $θ_{4}$	`theta4`	Its coefficient at $N$ sums $(- 1)^{N}$ at the integer roots of $j^{2} = N$ in $[- N, N]$ .
The Laurent summand with integer index	`term`	The source expression is retained literally after `HahnSeries.ofPowerSeries` embeds $A$ .
Normalization and every coefficient window	`IsGF`	Both normalization equalities and all $N, K$ with $N + 1 \leq K$ are required.
Every positive index; odd coefficient iff square	`claim`, `result`	Every normalized rational solution has an integer coefficient witness and the odd-square biconditional.
Signed residue iff square; divisibility otherwise	`claim`, `result`	The same coefficient witness satisfies the second biconditional and nonsquare divisibility.
Existence of the normalized series	First conjunct of `claim`	This strengthens the source convention by ruling out a vacuous universal assertion.
Rational-to-integer coefficient correspondence	Integer witness in `claim`	This proves integrality at every positive coefficient; it adds no hypothesis.

Motivation

This is an externally stated OEIS conjecture (tier 1). The single settling declaration is D5/S1/Recurrence/Bilateral/HannaThetaFourModFour.result; it carries the dossier’s sole OpenProblemResolutionClaim, with resolution Proved. The delivery uses deposit-uncovered, without an atom or coverage step.

Gap

The literature screen in #18830 records the OEIS entry, the research seat’s reading of its 18 revisions and the related A378582 and A002448 entries, repository and issue searches, and the named formal-conjecture indexes. No proof of these congruences was found in that searched scope. This is a scope-limited literature result, with completeness ASSUMED-UNVERIFIED.

The mathematical task is to connect the literal Laurent summands to an integral coefficient recursion and to identify every normalized rational solution with its integral solution.

Route

Write $A = XF$ and define the signed square source by $s_{k} = (- 1)^{k}$ when $k + 1$ is a square, and $s_{k} = 0$ otherwise. The private positive_factor and negative_factor identities normalize the positive and negative Laurent summands. Their exponents increase with the index; pair_order and tail_window justify each finite coefficient window.

The identities window_eq, theta_identity and gf_iff reduce the equation to $F = s + 4 T (F)$ , where $T$ is the integral series built from the normalized summand pairs. step_agree states that agreement below degree $d$ improves to agreement below degree $d + 1$ . The private diagonal construction solution satisfies this equation by solution_fixed. The generic frozen PowerSeriesNormalizedContraction.exists_unique_fixed, applied in fixed_unique, supplies uniqueness; gf_unique identifies every normalized rational solution with the rational image of the integer construction. solution_mod_four and arithmetic give the two square biconditionals and nonsquare divisibility in result.

The definitions theta4, term, IsGF and claim are literal matches to the binding conventions. Proofs use existing owners through private consumed adapters. There are no supporting modules or owner publications.

Falsifier

A normalized rational solution with a positive coefficient that is nonintegral, an odd coefficient at a nonsquare, an even coefficient at a square, a wrong signed square residue, or a nonsquare coefficient not divisible by four would contradict result. The theorem supplies a normalized solution, so an empty solution class cannot account for the result.

Evidence

Source note: Library/RecurrenceComposition/hanna2026a379764.md.
Lean owner: D5/S1/Recurrence/Bilateral/HannaThetaFourModFour.lean.
Public theorem: D5.S1.Recurrence.Bilateral.HannaThetaFourModFour.result.
Blueprint: Blueprint/D5/S1/Recurrence/Bilateral/HannaThetaFourModFour.md.
admission_basis: open-problem-resolution (#18830; Proved); generality: I; utility: none.
Public-theorem classification after expansion: result has proof_shape: bind-only, escape_witness: none. Admission is the external named problem’s settlement. The declarations are unbounded series identities and coefficient arguments, rather than finite numerical certificates.
The escape audit for D5.S1.Recurrence.Bilateral.HannaThetaFourModFour.result is unfinished: #19879. No validated four-slot registration is asserted. The missing evidence is a faithful reconstruction and realization bridge for the existence-plus-universal-coefficient proposition, an enrolled readout, actual-positive law, whole-family variation, slot sensitivity and observational dependence.

Experiment

Exact arithmetic checker and source data, commit 9dfe5bdc210cac281a148e7180239ddb21b0b34b. Command: python3 check.py in that directory; exit 0. Script SHA-256: ec87bb1637d6a946d4e5fb43f078bc623ce327257ef53b9305c05c564ca154b5. For A379764, the first 12 terms match the saved source data, the coefficients through degree 40 are integral, and both conjectures hold for $1 \leq n \leq 40$ . These are computed finite readings; the universal conclusion is supplied by result.

Triage

Lane target item	Status	Evidence
Settlement for the exact binding claim	Proved	Kernel-checked `D5.S1.Recurrence.Bilateral.HannaThetaFourModFour.result`: existence and all positive-index coefficient clauses.
The supplied mother-series route is realized directly by normalized positive/negative summands; no separate $Φ$ generalization or new task is needed	Proved for the stated route	Kernel-checked private `term_pos`, `term_neg`, `window_eq` and `gf_iff` implement the summand identities and reduction. This states the route used for this settlement, without asserting a new general $Φ$ theorem.
Finite arithmetic check	Computed	The pinned experiment above checks the first 12 terms and the exact scope $1 \leq n \leq 40$ .
Literature completeness	Open: `ASSUMED-UNVERIFIED`	The bounded screen recorded in #18830; no exhaustive priority claim.

What the settlement shows

Proved (kernel-checked): result gives a normalized rational solution and proves integrality, odd-square parity, the signed square-residue biconditional, and nonsquare divisibility for every normalized solution and every positive index. The decisive mechanism is the factor four in $F = s + 4 T (F)$ : its nonlinear correction vanishes modulo four. solution_mod_four, consumed by result, states that coefficient congruence for the integer construction.

Proved (kernel-checked auxiliary): gf_unique proves uniqueness of the normalized rational solution. No analytic convergence, arbitrary scaling parameter, or other OEIS generating equation is included in this statement.

Proved in prose from the definitions: the positive-index restriction cannot be extended unchanged to zero: normalization gives $a (0) = 0$ , which is even, whereas zero is a square. The defining generating equation and its normalization remain necessary hypotheses of the universal coefficient assertion.

Both conjectures in A379764 are settled under the coefficientwise interpretation above. The related mother-series entry A378582 supplies context; no additional claim about its other questions follows here. No separate $Φ$ generalization or additional task is proposed.

ASSUMED-UNVERIFIED

Literature-screen completeness, first-publication priority, and identification of the OEIS informal infinite sum with the stated coefficientwise finite-window convention are not Lean-kernel conclusions. The literature screen distinguishes the orchestrator’s direct checks from research-seat reports in #18830. The finite experiment is supporting arithmetic evidence, not a proof of the universal theorem. The four-slot escape audit remains unfinished as specified in #19879.

Keyboard shortcuts

trureturing — Discovering truth