MathDB
Romania EGMO TST 2022 Day 1 P2

Source:

February 15, 2022
romaniaEGMOcombinatorics

Problem Statement

At first, on a board, the number 11 is written 100100 times. Every minute, we pick a number aa from the board, erase it, and write a/3a/3 thrice instead. We say that a positive integer nn is persistent if after any amount of time, regardless of the numbers we pick, we can find at least nn equal numbers on the board. Find the greatest persistent number.