On the equation $N_{p_1}(E)\cdot N_{p_2}(E)\cdots N_{p_k}(E)=n$

Kirti Joshi

Published 2017-11-16Version 1

For a given elliptic curve $E/\mathbb{Q}$, set $N_p(E)$ to be the number of points on $E$ modulo $p$ for a prime of good reduction for $E$. Given integer $n$, let $G_k(E,n)$ be the number of $k$-tuples of pairwise distinct primes $p_1,\ldots,p_k$ of good reduction for $E$, for which equation in the title holds, then on assuming the Generalized Riemann Hypothesis for elliptic curves without CM (and unconditionally if the curves have complex multiplication), I show that $\varlimsup_{n\to\infty} G_k(E,n)=\infty$ for any integer $k\geq 3$. I also conjecture that this result also holds for $k=1$ and $k=2$. In particular for $k=1$ this conjecture says that there are "elliptic progressions of primes" i.e. sequences of primes $p_1<p_2\cdots <p_m$ of arbitrary lengths $m$ such that $N_{p_1}(E)=N_{p_2}(E)=\cdots =N_{p_m}(E)$.