Abstract
We develop a general framework for finding all perfect powers in sequences derived via shifting non-degenerate quadratic Lucas–Lehmer binary recurrence sequences by a fixed integer. By combining this setup with bounds for linear forms in logarithms and results based upon the modularity of elliptic curves defined over totally real fields, we are able to answer a question of Bugeaud, Luca, Mignotte and the third author by explicitly finding all perfect powers of the shape \(F_k \pm 2 \) where \(F_k\) is the k-th term in the Fibonacci sequence.
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Acknowledgements
The first-named is supported by NSERC. The third-named author is supported by an EPSRC Leadership Fellowship EP/G007268/1, and EPSRC LMF: L-Functions and Modular Forms Programme Grant EP/K034383/1.
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Bennett, M.A., Patel, V. & Siksek, S. Shifted powers in Lucas–Lehmer sequences. Res. number theory 5, 15 (2019). https://doi.org/10.1007/s40993-019-0153-2
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DOI: https://doi.org/10.1007/s40993-019-0153-2
Keywords
- Exponential equation
- Lucas sequence
- shifted power
- Galois representation
- Frey curve
- modularity
- Level lowering
- Baker’s bounds
- Hilbert modular forms
- Thue equation