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What is the smallest perfect square that ends with the four digits 9009?

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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?

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Mod 7

Find the remainder when 3^{2001} is divided by 7.


Age 16 to 18 Challenge Level:

This example is merely an introduction to the subject to introduce the idea of devising formulae with corresponding deciphering formulae to encipher and decipher text automatically.