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Dirisibly Yours
Age 16 to 18
Challenge Level 
We wonder who can find and explain the shortest and neatest proof that
$5^{2n+1} + 11^{2n+1} + 17^{2n+1}$
is divisible by 33 for every non negative integer n .
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Old Nuts
In turn 4 people throw away three nuts from a pile and hide a quarter of the remainder finally leaving a multiple of 4 nuts. How many nuts were at the start?
