Bruckman–Anderson conjecture on the density of Fibonacci entry-point divisibility

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Let F0=0F_0=0, F1=1F_1=1, and Fn=Fn−1+Fn−2F_n=F_{n-1}+F_{n-2} for n≥2n\geq 2 be the Fibonacci sequence. For a prime pp, let Z(p)Z(p) be the smallest positive integer mm such that p∣Fmp\mid F_m. For a positive integer mm, define

M(m,x)=#{p≤x:p is prime and m∣Z(p)},M(m,x)=\#\{p\leq x:p\text{ is prime and }m\mid Z(p)\},

and

ζ(m)=lim⁡x→∞M(m,x)π(x),\zeta(m)=\lim_{x\to\infty}\frac{M(m,x)}{\pi(x)},

when this limit exists. For a prime power qeq^e with e≥1e\geq 1, and for an arbitrary positive integer mm, define

ρ(m)={1if 10∤m,54if m≡10(mod20),12if 20∣m.\rho(m)=\begin{cases}1&\text{if }10\nmid m,\\[2pt]\frac54&\text{if }m\equiv10\pmod{20},\\[2pt]\frac12&\text{if }20\mid m.\end{cases}

Bruckman–Anderson conjecture. If m=qem=q^e is a prime power with e≥1e\geq 1, then

ζ(qe)=q2−eq2−1.\zeta(q^e)=\frac{q^{2-e}}{q^2-1}.

For an arbitrary positive integer mm,

ζ(m)=ρ(m)∏qj∥mζ(qj),\zeta(m)=\rho(m)\prod_{q^j\parallel m}\zeta(q^j),

where the product is over all prime powers occurring in the prime factorization of mm. The conjecture gives the expected density of primes whose Fibonacci entry point is divisible by mm, refining the known density 2/32/3 for even Fibonacci entry points. The source presents this as a conjecture based on numerical data; its resolution is not stated here.

References

Primary source

Paul Cubre and Jeremy Rouse, “Divisibility properties of the Fibonacci entry point”, arXiv:1212.6221 (2012).

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