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Identical bikes and a total spoke count

Question

A shop has at least 22 bikes, all identical; each wheel has at least one spoke, but a bike's front and rear wheels may differ. The shop's total spoke count is between 200200 and 300300. You are told that, if you learned that total, you could deduce the number of bikes for certain. That fact alone lets you work out how many bikes there are. How many?

Short answer

1717. The total is N=b⋅sN=b\cdot s with b≥2b\ge2 bikes and s≥2s\ge2 spokes per bike. The bike count is determined only if NN has exactly one such factorisation, which happens only when N=p2N=p^2 for a prime pp. The only one in [200,300][200,300] is 289=172289=17^2, so there are 1717 bikes.

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