2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/230106It is shown, subject to the abc-conjecture, that \[\sum_{n\le N}\exp(2πiαn^3)\ll_{ε,α}N^{5/7+ε}\] for any $ε>0$ and any quadratic irrational $α$.Number Theory11L15text