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What is the units digit for the number 123^(456) ?

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How many noughts are at the end of these giant numbers?

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Novemberish

a) A four digit number (in base 10) aabb is a perfect square. Discuss ways of systematically finding this number. (b) Prove that 11^{10}-1 is divisible by 100.

Mod 3

Age 14 to 16 Challenge Level:

Prove that if $a^2+b^2$ is a multiple of $3$ then both $a$ and $b$ are multiples of $3$.