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Start with any number of counters in any number of piles. 2 players take it in turns to remove any number of counters from a single pile. The loser is the player who takes the last counter.

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Back to Basics

Find b where 3723(base 10) = 123(base b).

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Nim-like Games

A collection of games on the NIM theme

Composite Notions

Stage: 4 Challenge Level: Challenge Level:3 Challenge Level:3 Challenge Level:3

The following solution was recieved from Andrei of School 205 Bucharest. Well done and thank you Andrei.
 

10201 could be written (in base $x$) as:

$$\begin{align*}10201 &= 1x^0 + 2x^2 + 1x^4 \\ &= x^4 + 2x^2 + 1 \\ &= (x^2 + 1)^2 \end{align*}$$

Now, I write 10101 in a similar manner, in base $y$:

$$\begin{align*} 10101& = y^4 + y^2 + 1\\ & = y^4 + 2y^2 - y^2 + 1\\ & = (y^4 + 2y^2 + 1) - y^2\\ & = (y^2 + 1)^2 - y^2\\ & = (y^2 + 1 + y)(y^2 + 1 -y) \end{align*}$$

Therefore both expressions can be factorised, so they are composite.