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A277129
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Largest m < n such that 2^m == 2^n (mod n).
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0
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0, 1, 1, 3, 1, 4, 4, 7, 3, 6, 1, 10, 1, 11, 11, 15, 9, 12, 1, 16, 15, 12, 12, 22, 5, 14, 9, 25, 1, 26, 26, 31, 23, 26, 23, 30, 1, 20, 27, 36, 21, 36, 29, 34, 33, 35, 24, 46, 28, 30, 43, 40, 1, 36, 35, 53, 39, 30, 1, 56, 1, 57, 57, 63, 53, 56, 1, 60, 47, 58, 36, 66, 64, 38, 55, 58, 47, 66, 40, 76, 27, 62, 1
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OFFSET
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1,4
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COMMENTS
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If n is odd, then a(n) = n - A002326((n-1)/2).
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LINKS
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MATHEMATICA
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Table[m = n - 1; While[Mod[2^m, n] != Mod[2^n, n], m--]; m, {n, 83}] (* Michael De Vlieger, Oct 02 2016 *)
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PROG
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(PARI) a(n) = {if(n==0, return(0)); my(pt = valuation(n, 2), odd = n/2^pt, ul = odd-A002326(odd\2)); forstep(i = n-1, ul, -1, if(Mod(2, n)^i==Mod(2, n)^n, return(i)))} \\ David A. Corneth, Oct 01 2016
A002326(n)=if(n<0, 0, znorder(Mod(2, 2*n+1)))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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