English

Equal sums of two cubes of binary quadratic forms

Number Theory 2020-02-04 v1 Algebraic Geometry

Abstract

We give a complete description of all solutions to the equation f13+f23=f33+f43f_1^3 + f_2^3 = f_3^3 + f_4^3 for quadratic forms fjC[x,y]f_j \in \mathbb C[x,y] and show how Ramanujan's example can be extended to three equal sums of pairs of cubes. We also give a complete census in counting the number of ways a sextic pC[x,y]p \in \mathbb C[x,y] can be written as a sum of two cubes. The extreme example is p(x,y)=xy(x4y4)p(x,y) = xy(x^4-y^4), which has six such representations.

Keywords

Cite

@article{arxiv.2002.00888,
  title  = {Equal sums of two cubes of binary quadratic forms},
  author = {Bruce Reznick},
  journal= {arXiv preprint arXiv:2002.00888},
  year   = {2020}
}

Comments

Submitted to International Journal of Number Theory, for the Special Issue on the Berndt Conference Proceedings

R2 v1 2026-06-23T13:29:34.336Z