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A126717
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Least odd k such that k*2^n-1 is prime.
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6
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3, 3, 1, 1, 3, 1, 3, 1, 5, 7, 5, 3, 5, 1, 5, 9, 17, 1, 3, 1, 17, 7, 33, 13, 39, 57, 11, 21, 27, 7, 213, 1, 5, 31, 3, 25, 17, 21, 3, 25, 107, 15, 33, 3, 35, 7, 23, 31, 5, 19, 11, 21, 65, 147, 5, 3, 33, 51, 77, 45, 17, 1, 53, 9, 3, 67, 63, 43, 63, 51, 27, 73, 5, 15, 21, 25, 3, 55, 47, 69
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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LINKS
| T. D. Noe, Table of n, a(n) for n=0..1000
Yves Gallot's Proth search page
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EXAMPLE
| a(10)=5 because 5*2^10-1 is prime but 1*2^10-1 and 3*2^10-1 are not.
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MATHEMATICA
| f[n_] := Block[{k = 1}, While[ !PrimeQ[k*2^n - 1], k += 2]; k]; Table[f@n, {n, 0, 80}] - Robert G. Wilson v (rgwv(at)rgwv.com), Feb 20 2007
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CROSSREFS
| Cf. A035050, A057778, A085427.
Sequence in context: A178395 A021306 A125300 * A124039 A096433 A084101
Adjacent sequences: A126714 A126715 A126716 * A126718 A126719 A126720
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KEYWORD
| nonn
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AUTHOR
| Bernardo Boncompagni (redgolpe(AT)redgolpe.com), Feb 13 2007
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EXTENSIONS
| More terms from Robert G. Wilson v (rgwv(at)rgwv.com), Feb 20 2007
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