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A224486
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Numbers k such that 2*k+1 divides 2^k+1.
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5
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1, 2, 5, 6, 9, 14, 18, 21, 26, 29, 30, 33, 41, 50, 53, 54, 65, 69, 74, 78, 81, 86, 89, 90, 98, 105, 113, 114, 125, 134, 138, 141, 146, 153, 158, 165, 173, 174, 186, 189, 194, 198, 209, 210, 221, 230, 233, 245, 249, 254, 261, 270, 273, 278, 281, 285, 293
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OFFSET
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1,2
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COMMENTS
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The numbers are called Curzon numbers by Tattersall (p. 85, exercise 43).
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REFERENCES
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James J. Tattersall, Elementary Number Theory in Nine Chapters, Second Edition, Cambridge University Press, 2005, p. 85.
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LINKS
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EXAMPLE
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5 is in the list since 2*5 + 1 = 11 divides 2^5 + 1 = 33.
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MATHEMATICA
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Select[Range[300], PowerMod[2, #, 2 # + 1] == 2 # &] (* Amiram Eldar, Oct 13 2020 *)
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PROG
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(PARI) for(n=0, 10^3, my(m=2*n+1); if( Mod(2, m)^n==Mod(-1, m), print1(n, ", ") ) ); \\ Joerg Arndt, Apr 08 2013
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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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