Auxiliary solution-count conjectures for the discrete logarithm equation

From papers

Let pp be prime. For the auxiliary equation studied in the paper, let ChA,aB(p)C_{h\,A,a\,B}(p) denote the number of solutions with the indicated restrictions, and let ϕ\phi be Euler's totient function. If p1p-1 is squarefree, write its prime divisors as qq; in general write qαp1q^\alpha\Vert p-1 when qαq^\alpha is the exact power of qq dividing p1p-1.

Auxiliary solution-count conjectures.

ChANY,aANY(p)(p1)+mp1ϕ(m)m2(d(p1)/mϕ(dm)d)2.C_{h\,\mathsf{ANY},a\,\mathsf{ANY}}(p)\approx (p-1)+\sum_{m\mid p-1}\frac{\phi(m)}{m^2}\left(\sum_{d\mid (p-1)/m}\frac{\phi(dm)}{d}\right)^2.

If p1p-1 is squarefree, then

ChANY,aANY(p)(p1)+qp1(q+11q).C_{h\,\mathsf{ANY},a\,\mathsf{ANY}}(p)\approx (p-1)+\prod_{q\mid p-1}\left(q+1-\frac1q\right).

In general,

ChANY,aANY(p)(p1)+qαp1([(11q)α+1]2+(11q)3[(α+1)2qα+1qq12(α+1)αqα+2(α+1)qα+1+q(q1)2+α2qα+3(2α2+2α1)qα+2+(α2+2α+1)qα+1q2q(q1)3]).C_{h\,\mathsf{ANY},a\,\mathsf{ANY}}(p)\approx (p-1)+\prod_{q^\alpha\Vert p-1}\left(\left[\left(1-\frac1q\right)\alpha+1\right]^2+\left(1-\frac1q\right)^3\left[(\alpha+1)^2\frac{q^{\alpha+1}-q}{q-1}-2(\alpha+1)\frac{\alpha q^{\alpha+2}-(\alpha+1)q^{\alpha+1}+q}{(q-1)^2}+\frac{\alpha^2q^{\alpha+3}-(2\alpha^2+2\alpha-1)q^{\alpha+2}+(\alpha^2+2\alpha+1)q^{\alpha+1}-q^2-q}{(q-1)^3}\right]\right).

The product is over primes qq dividing p1p-1. Additionally,

ChPR,aANY(p)2ϕ(p1),C_{h\,\mathsf{PR},a\,\mathsf{ANY}}(p)\approx 2\phi(p-1), ChANY,aPR(p)2ϕ(p1),C_{h\,\mathsf{ANY},a\,\mathsf{PR}}(p)\approx 2\phi(p-1), ChPR,aPR(p)ϕ(p1)+ϕ(p1)2p1.C_{h\,\mathsf{PR},a\,\mathsf{PR}}(p)\approx \phi(p-1)+\frac{\phi(p-1)^2}{p-1}.

These predictions are derived from the paper's random-map heuristic for xxxmodpx\mapsto x^x\bmod p and remain conjectural in the supplied text.

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Sources & referencesView supporting material

Primary source

Joshua Holden and Pieter Moree, “Some Heuristics and Results for Small Cycles of the Discrete Logarithm”, arXiv:math/0401013 (2004).

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