Problem

Source: 2024 imocsl C7 (Night 4-C)

Tags: combinatorics, IMOC



On a plane there is an invisible rabbit (rabbit) hiding on a lattice point. We want to put $n$ hunters on some lattice points to catch the rabbit. In a turn each hunter can choose to shoot to left/right or top/bottom direction. On the $i$th turn there will be these steps in order 1. The rabbit jumps to an adjacent lattice point on the top, bottom, left, or right. 2. item Each hunter moves to an adjacent lattice point on the top, bottom, left or right (each hunter can move to different direction). Then they shoot a bullet which travels $\frac{334111214}{334111213}i$ units on the directions they chose. If a bullet hits the rabbit then it is caught. Find the smallest number $n$ such that the rabbit would definitely be caught in a finite number of turns. Proposed by tob8y