An infinite game (noch nicht übersetzt)

Problem 664

Peter is playing a solitaire game on an infinite checkerboard, each square of which can hold an unlimited number of tokens.

Each move of the game consists of the following steps:

  1. Choose one token T to move. This may be any token on the board, as long as not all of its four adjacent squares are empty.
  2. Select and discard one token D from a square adjacent to that of T.
  3. Move T to any one of its four adjacent squares (even if that square is already occupied).
Allowed moves

The board is marked with a line called the dividing line. Initially, every square to the left of the dividing line contains a token, and every square to the right of the dividing line is empty:

Initial setup

Peter's goal is to get a token as far as possible to the right in a finite number of moves. However, he quickly finds out that, even with his infinite supply of tokens, he cannot move a token more than four squares beyond the dividing line.

Peter then considers starting configurations with larger supplies of tokens: each square in the dth column to the left of the dividing line starts with dn tokens instead of 1. This is illustrated below for n=1:

Initial setup n=1

Let F(n) be the maximum number of squares Peter can move a token beyond the dividing line. For example, F(0)=4. You are also given that F(1)=6, F(2)=9, F(3)=13, F(11)=58 and F(123)=1173.

Find F(1234567).