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A301759
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Semiperiods of the Fibonacci sequence mod n.
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1
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1, 3, 4, 6, 10, 12, 8, 12, 12, 30, 10, 24, 14, 24, 40, 24, 18, 12, 18, 60, 16, 30, 24, 24, 50, 42, 36, 48, 14, 120, 30, 48, 40, 18, 80, 24, 38, 18, 56, 60, 20, 48, 44, 30, 120, 24, 16, 24, 56, 150, 72, 84, 54, 36, 20, 48, 72, 42, 58, 120, 30, 30, 48, 96, 70, 120, 68, 36, 48
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OFFSET
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1,2
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COMMENTS
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It is the period of the Fibonacci sequence up to sign.
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LINKS
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EXAMPLE
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For n = 7 we get 1,0,1,1,2,3,5,1,-1,0,-1,-1,... so a(7) = 8.
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MATHEMATICA
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Table[NestWhile[# + 1 &, 1, ! (Mod[Fibonacci[#], n] == 0 && With[{f = Mod[Fibonacci[# + 1], n]}, f == 1 || f == n - 1]) &], {n, 69}] (* Jan Mangaldan, Sep 12 2021 *)
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PROG
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(PARI) a(n) = if (n==1, 1, for(k=1, oo, if (((fibonacci(k) % n) == 0) && (((fibonacci(k+1) % n) == 1) || ((fibonacci(k+1) % n) == n-1)), return (k))));
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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