On perfect powers that are sums of cubes of a nine term arithmetic progression

TL;DR

This paper investigates a specific sum of nine cubes in an arithmetic progression equaling a perfect power, establishing conditions for solutions and constructing infinite solutions for certain exponents using advanced number theory techniques.

Contribution

It extends previous work on sums of cubes in arithmetic progressions by analyzing a nine-term case and providing explicit solutions for quadratic and cubic powers.

Findings

Solutions must satisfy xy=0 under certain conditions

Infinite solutions exist for p=2 and p=3 with specific constructions

Utilizes advanced computational and algebraic number theory methods

Abstract

We study the equation $(x-4r)^3 + (x-3r)^3 + (x-2r)^3+(x-r)^3 + x^3 + (x+r)^3+(x+2r)^3 + (x+3r)^3 + (x+4r)^3 = y^p$, which is a natural continuation of previous works carried out by A. Arg\'{a}ez-Garc\'{i}a and the fourth author (perfect powers that are sums of cubes of a three, five and seven term arithmetic progression). Under the assumptions $0 < r \leq 10^6$, $p \geq 5 $ a prime and $\gcd(x, r) = 1$, we show that solutions must satisfy $xy=0$. Moreover, we study the equation for prime exponents $2$ and $3$ in greater detail. Under the assumptions $r>0$ a positive integer and $\gcd(x, r) = 1$ we show that there are infinitely many solutions for $p=2$ and $p=3$ via explicit constructions using integral points on elliptic curves. We use an amalgamation of methods in computational and algebraic number theory to overcome the increased computational challenge. Most notable is a significant computational efficiency obtained through appealing to Bilu, Hanrot and Voutier's Primitive Divisor Theorem and the method of Chabauty, as well as employing a Thue equation solver earlier on.