MathDB
Sum of all possible values of winning strategy in a game

Source: Bangladesh Mathematical Olympiad 2021 Problem 8

February 26, 2022
combinatorics

Problem Statement

Shakur and Tiham are playing a game. Initially, Shakur picks a positive integer not greater than 10001000. Then Tiham picks a positive integer strictly smaller than that.Then they keep on doing this taking turns to pick progressively smaller and smaller positive integers until some one picks 11. After that, all the numbers that have been picked so far are added up. The person picking the number 11 wins if and only if this sum is a perfect square. Otherwise, the other player wins. What is the sum of all possible values of nn such that if Shakur starts with the number nn, he has a winning strategy?