Abstract

In a recent paper, Chatterjee, the author and Mohan posed the problem of determining all solutions of the Diophantine equation Fn=Φ(m)F_n=Φ(m), where FnF_n is the nn-th Fibonacci number and Φ(m)Φ(m) counts the number of nonempty sets A{1,2,,m}A \subseteq \{1, 2, \dots, m\} for which gcd(A)\gcd(A) is relatively prime to mm. In this paper, we prove that the Diophantine equation has the only solutions (n,m)=(1,1),(2,1),(3,2)(n,m)=(1,1),(2,1),(3,2). The main tools used in this paper are lower bounds for linear forms in logarithms due to Matveev and Dujella-Peth{ő} version of the Baker-Davenport reduction method in diophantine approximation.

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Audit summary

Audited against arXiv v1

Not a correctness certificate. A “Correct” result may include yellow typos or minor formal corrections that do not affect substantive soundness. It means this audit found no unresolved substantive error under the stated criteria; it does not replace expert scrutiny or formal verification.

Current report

Detailed mathematical audit

Generated August 15, 2026
01Statements1 reported findingCorrect

The classification Fn=Φ(m)F_n=\Phi(m) with solutions (n,m)=(1,1),(2,1),(3,2)(n,m)=(1,1),(2,1),(3,2) is correct. The analytic reduction and both terminal searches were independently reproduced.

Theorem 1.2Correct

Complete solution of Fn=Φ(m)F_n=\Phi(m)

Pages 2–7 · Theorem 1.2 and Section 3 · arXiv:2606.24908v1

For m79m\geq79, divisibility gives n=12kn=12k and the Matveev estimate gives k<1.911014k<1.91\cdot10^{14}. Recomputing the Dujella–Pethő iteration with the stated continued fraction of log2/logφ\log2/\log\varphi reduces this bound beyond the paper's k163k\leq163 endpoint. Exact evaluation of Φ(m)=dmμ(d)2m/d\Phi(m)=\sum_{d\mid m}\mu(d)2^{m/d} then finds no solution for 79m<12k79\leq m<12k in that range, and the exact search for m78m\leq78 returns only the three displayed pairs.

02Proofs2 reported findingsCorrect

The proof is correct and complete. Its decisive continued-fraction iteration and brute-force exclusions are reproducible from the displayed inequalities. The printed decimal values of ϵ\epsilon are inaccurate, but the actual values are positive and give the same stated reductions.

Proof of Theorem 1.2Correct and complete

Linear-form reduction and exact finite search

Pages 3–7 · Equations (4)–(5) and final computation · arXiv:2606.24908v1

Lemma 3.1 controls the non-leading divisor terms, Matveev's theorem supplies the initial effective bound, and Lemma 2.2 applies with u=mu=m, w=12kw=12k, and M=12KM=12K at each current upper bound KK. An independent high-precision implementation reproduces the first three displayed bounds exactly and reaches an even stronger fixed bound; exact integer searches then verify both terminal exclusions.

Numerical typoTypo

The displayed ϵ\epsilon values omit the subtraction term

Pages 5–6 · four applications of Lemma 2.2 · arXiv:2606.24908v1

For the first use of q=54471843954966727q=54471843954966727 and M=2.2921015M=2.292\cdot10^{15}, the definition gives ϵ=μqMγq0.4577589626\epsilon=\|\mu q\|-M\|\gamma q\|\approx0.4577589626, not 0.487250.48725\ldots; the latter is μq\|\mu q\| alone. The later repeated decimals have the same transcription error. In every displayed application the correctly computed ϵ\epsilon remains positive, and using it reproduces the paper's successive integer bounds, so this typo does not affect the proof or status.

03Novelty0 reported findingsNo non-novelty findings

No non-novelty findings.

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Paper
arXiv:2606.24908v1
Authors listed
Sagar Mandal
Audit date
August 15, 2026
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