English

Fibonacci numbers modulo cubes of primes

Number Theory 2013-11-01 v9 Combinatorics

Abstract

Let pp be an odd prime. It is well known that Fp(p5)0(modp)F_{p-(\frac p5)}\equiv 0\pmod{p}, where {Fn}n0\{F_n\}_{n\ge0} is the Fibonacci sequence and ()(-) is the Jacobi symbol. In this paper we show that if p5p\not=5 then we may determine Fp(p5)F_{p-(\frac p5)} mod p3p^3 in the following way: k=0(p1)/2(2kk)(16)k(p5)(1+Fp(p5)2)(modp3).\sum_{k=0}^{(p-1)/2}\frac{\binom{2k}k}{(-16)^k}\equiv\left(\frac{p}5\right)\left(1+\frac{F_{p-(\frac {p}5)}}2\right)\pmod{p^3}. We also use Lucas quotients to determine k=0(p1)/2(2kk)/mk\sum_{k=0}^{(p-1)/2}\binom{2k}k/m^k modulo p2p^2 for any integer m≢0(modp)m\not\equiv0\pmod{p}; in particular, we obtain k=0(p1)/2(2kk)16k(3p)(modp2).\sum_{k=0}^{(p-1)/2}\frac{\binom{2k}k}{16^k}\equiv\left(\frac3{p}\right)\pmod{p^2}. In addition, we pose three conjectures for further research.

Keywords

Cite

@article{arxiv.0911.3060,
  title  = {Fibonacci numbers modulo cubes of primes},
  author = {Zhi-Wei Sun},
  journal= {arXiv preprint arXiv:0911.3060},
  year   = {2013}
}

Comments

21 pages. Final published version

R2 v1 2026-06-21T14:12:13.594Z