Arash and Babak L-corners squares
Source: Iran MO Third Round 2021 F4
September 25, 2021
combinatorics
Problem Statement
Arash and Babak play the following game, taking turns alternatively, on a table. Arash starts and in his turns he colors , -corners (any three cell of a square). Babak in his turn colors one square. Neither player is allowed to recolor any cell. Find all positive integers for which Arash has a winning strategy.