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CMO 1997 Problem 5

  • Day 2

Let A={1,2,3,⋯ ,17}A=\{1,2,3,\cdots ,17\} . A mapping f:A→Af:A\rightarrow A is defined as follows: f[1](x)=f(x),f[k+1](x)=f(f[k](x))f^{[1]}(x)=f(x), f^{[k+1]}(x)=f(f^{[k]}(x)) for k∈Nk\in\mathbb{N} . Suppose that ff is bijective and that there exists a natural number MM such that: i) when m<Mm<M and 1≤i≤161\le i\le 16 , we have f[m](i+1)−f[m](i)≠±1(mod17)f^{[m]}(i+1)- f^{[m]}(i) \not=\pm 1\pmod{17} and f[m](1)−f[m](17)≠±1(mod17)f^{[m]}(1)- f^{[m]}(17) \not=\pm 1\pmod{17} ; ii) when 1≤i≤161\le i\le 16 , we have f[M](i+1)−f[M](i)=±1(mod17)f^{[M]}(i+1)- f^{[M]}(i)=\pm 1 \pmod{17} and f[M](1)−f[M](17)=±1(mod17)f^{[M]}(1)- f^{[M]}(17)=\pm 1\pmod{17} . Find the maximal value of MM .

Dataset text AI-MO AoPS. Quoted with source.

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