and play a game, given an integer , writes down first, then every player sees the last number written and if it is then in his turn he writes or , but his number cannot be bigger than . The player who writes wins. For which values of does win?
*
and play a game, given an integer , writes down first, then every player sees the last number written and if it is then in his turn he writes or , but his number cannot be bigger than . The player who writes wins. For which values of does win?
*
To determine for which values of player wins, we need to analyze the structure of the game and identify a strategy that ensures victory for player .
### Game Analysis
Given the rules of the game:
- Player starts by writing the number .
- Each player alternates turns writing either or , where is the last number written.
- The number written cannot exceed .
- The player who writes wins.
To solve the problem, we must deduce for which values of , player is guaranteed a win regardless of how optimally player \( A \ plays.
### Winning and Losing Positions
In combinatorial game theory, we identify "winning" and "losing" positions:
- Winning Position: A position where the player whose turn it is can force a win with optimal play.
- Losing Position: A position where the player whose turn it is will lose with optimal play from the opponent.
The strategy involves determining the losing positions. Player will win if and only if begins his turn in a losing position.
### Characterizing Losing Positions
1. Base Case:
- is a losing position because player starts and immediately wins.
2. Recursive Analysis:
- If writing is a losing position, then both and must be winning positions.
- Conversely, is a winning position if either or is a losing position.
By iteratively applying these conditions, we can deduce:
- A position is losing if is the sum of distinct odd powers of 2. These are numbers whose binary representation consists of zeros and a single one in an odd position.
### Examples and Verification
For example, consider .
- is losing (as defined above).
- Starting from 1, player can choose 2.
- Then, player can choose 3 and win. Hence, 3 was a winning position for .
Values of being sums of distinct odd powers of 2 include . In binary, these are 1, 11, 101, 1001, 10001, corresponding to .
### Final Conclusion
Player wins for values of that are sums of distinct odd powers of 2. Therefore, the answer is:
This strategy ensures that player will always find themselves in a winning position when fits this pattern. The correct identification of such solidifies player 's chances of winning.