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Show by combinatoric means that ##p\,|\,(a^p-a) ## for a prime ##p \in \mathbb{P}## and a positive integer ##a\in\mathbb{N}##.
Hint: e.g. consider chains of ##p## coloured pearls where ##a## is the number of colours.
Hint: e.g. consider chains of ##p## coloured pearls where ##a## is the number of colours.