Metadata

slug: bala-a258899-totient-period
bibkey: bala2025a258899a258903
doi: null
url: https://oeis.org/A258899
triage: theorem
motivation_gids:
  - D5/S1/Recurrence/Periodic/BalaDivisorFactorialTotientPeriod.result

Bala’s A258899 and A258903 totient-period conjectures

Problem

Peter Bala’s COMMENTS conjecture for OEIS A258899 and A258903 states:

Conjecture: the sequence a(n) taken modulo a positive integer k is eventually periodic with the period dividing phi(k).

The two sequences use the FORMULA fields

$a_{899} (n) = d ∣ n \sum 2^{d} \frac{n !}{d ! ( n / d )!}, a_{903} (n) = d ∣ n \sum 2^{d} 3^{n / d} \frac{n !}{d ! ( n / d )!}$

for $n \geq 1$ , with value $1$ at index zero. The settling declaration states the two eventual-period assertions literally, with natural-number division and Nat.ModEq.

For each positive natural modulus $m$ , the result supplies an onset $N$ , a positive natural period $T$ dividing Nat.totient m, and the congruence for every $n \geq N$ , separately for A258899 and A258903.

Motivation

The source entries are OEIS A258899 and A258903, revisions recorded in the literature note D5/L/RecurrenceComposition/bala2025a258899a258903. The problem was preregistered in issue #24054 before the formal proof.

Gap

The source marked both eventual-period assertions as conjectures. The bounded literature screen recorded in #24054 found no inspected source settling either target. Literature completeness is ASSUMED-UNVERIFIED.

Route

For $n \geq 2 m + 4$ , a proper factorization $n = d e$ with $d, e \geq 2$ gives $d + e + m \leq n$ . Factorial divisibility then makes $m$ divide the factorial quotient, so only $d = 1$ and $d = n$ survive modulo $m$ . For arbitrary natural weights $u, v$ , the surviving terms are $u v^{n} + v u^{n}$ . The imported theorem D5.S1.Recurrence.Periodic.StirlingTransformTotientPeriod.pow_add_totient makes both powers unchanged after a shift by $totient (m)$ . The weights $(2, 1)$ and $(2, 3)$ give the two source sequences, with $N = 2 m + 4$ and $T = totient (m)$ .

Falsifier

A modulus and tail index satisfying the hypotheses but violating either displayed Nat.ModEq conclusion would refute the settlement. A smaller uniform onset or period may sharpen the result but does not refute it.

Evidence

The kernel-checked settling declaration is D5/S1/Recurrence/Periodic/BalaDivisorFactorialTotientPeriod.result; its module state is Golden/Frozen/state/D5/S1/Recurrence/Periodic/BalaDivisorFactorialTotientPeriod.lean.json. The scoped Lean report records the public declaration axiom closure inside {propext, Classical.choice, Quot.sound}.

Independent finite checks are published in the experiments repository at commit 96efa433d49769b9ab2f8e0fb1263b9ca0725b6e, path docs/reports/bala-a258899-a258903/check.py. The script SHA-256 is 12c906c780a8b964892bf4dfe987eb5254ed0c2e089260d72b6999a1309a016a. The command python3 docs/reports/bala-a258899-a258903/check.py exits 0 with ALL_CHECKS_OK; it checks the finite ranges reported by the source program and is not the universal proof.

Four-slot escape auditing is unfinished for D5/S1/Recurrence/Periodic/BalaDivisorFactorialTotientPeriod.result; issue #25641 records the missing lawful registration evidence. No declared_validated or DTR-Declared status is claimed before the required CI reading.

Triage

The settlement is Proved by D5/S1/Recurrence/Periodic/BalaDivisorFactorialTotientPeriod.result. Its proof shape is bind-only after helper expansion; the admission basis is open-problem-resolution (#24054; Proved).

item	status	evidence
Mechanism: proper-factor terms vanish for $n \geq 2 m + 4$ , leaving the two explicit exponential tails	proved	Kernel-checked `...result`, using the consumed factorial-divisibility and divisor-tail helpers.
Extension and surviving neighbours: the tail formula and totient shift hold for every natural pair $(u, v)$ , including zero	proved	The same kernel-checked result’s consumed general-weight tail and period steps.
Common witnesses: both source sequences use $N = 2 m + 4$ and $T = totient (m)$ , including $m = 1$	proved	Kernel-checked `...result` supplies those witnesses and `Nat.totient_pos`.
Independent finite checks: 43,350 proper terms, 168,960 generic tails, 151,328 totient shifts, and 242,088 power periods on the script’s finite ranges	computed	`python3 docs/reports/bala-a258899-a258903/check.py`, exit 0, script SHA-256 above; finite checks are not the universal proof.
Sharp bounds: least onset or least eventual period for each modulus and weight pair	open	No declaration in this delivery addresses minimality.
Literature completeness	open	`ASSUMED-UNVERIFIED`; the inspected source set does not establish exhaustive coverage.

What the settlement shows

The decisive mechanism is factorial divisibility for proper factors after the explicit onset, followed by the existing totient power-period theorem. The argument extends to arbitrary natural weights, removes any positivity requirement on the weights, includes modulus one, and supplies common witnesses for both OEIS sequences. The least possible onset and least eventual period remain open.

ASSUMED-UNVERIFIED

Literature completeness is ASSUMED-UNVERIFIED; unsearched full texts and rate-limited indices remain outside the inspected scope. Escape registration remains unfinished under issue #25641 until a lawful typed registration and its required CI DTR reading exist.

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