MathDB
n=sum of a perfect square plus a perfect cube

Source: Argentina 2005 OMA L3 p4

May 12, 2024
number theoryperfect cubePerfect Squaregeometry3D geometry

Problem Statement

We will say that a positive integer is a winner if it can be written as the sum of a perfect square plus a perfect cube. For example, 3333 is a winner because 33=52+2333=5^2+2^3 . Gabriel chooses two positive integers, r and s, and Germán must find 20052005 positive integers nn such that for each nn, the numbers r+nr+n and s+ns+n are winners. Prove that Germán can always achieve his goal.