Ponder This Challenge - February 2026 - Blot-avoiding backgammon strategy
- Ponder This
Ponder This Challenge:
Two players starts with the number N and play in turns.
In each turn the player chooses a prime power p^m>1, which divides N and updates N to be N/(p^m).
The player who sets N to be 1 - wins.
What are all the winning moves from the initial state of N=1,506,009,006,001,500,000,000 ?
Update 6/8: We are looking for all the moves the first player can make which, assuming he plays correctly, can guarantee him winning the game.
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First we factor 1,506,009,006,001,500,000,000.
It is easy to factor out 10^8=2^8 * 5^8 and then 15=3*5.
Noticing the binomial coefficients in the result (1,004,006,004,001) we get 1001^4=7^4 * 11^4 * 13^4.
So the factorization of N is 2^8 * 3^1 * 5^9 * 7^4 * 11^4 * 13^4.
Then we note that the game is a actually the classic game of Nim in disguise.
The winning moves from the initial state of (8,1,9,4,4,4) are to remove one of the piles of 4.
Translating it back to our game - the winning moves are 7^4, 11^4 and 13^4.
Sec Zehl (06/01/2012 01:59 PM EDT)