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A194637
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Record values in A194636.
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12
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0, 1, 2, 4, 5, 6, 11, 18, 20, 28, 70, 106, 150, 726, 2906, 7431, 14073, 22394, 41422, 82587, 85461, 356981
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,3
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COMMENTS
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The index sequence is 1, 3, 7, 24, 30, 55, 121, 168, 555, 687, 724, 7447, 26134, 28272, 324802, 419221, 4420051, 8467881, 50302257, 59186640, 135352084, 677738616, ... given by formula (A194639(n)+1)/2.
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REFERENCES
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Wilfrid Keller, personal communication, 2010.
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LINKS
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FORMULA
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EXAMPLE
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MATHEMATICA
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l = -1; Flatten[Table[n = 2*n - 1; k = 0; While[! PrimeQ[n*2^k - 1] && ! PrimeQ[n*2^k + 1], k++]; If[k > l, l = k, {}], {n, 10^5}]] (* Arkadiusz Wesolowski, Sep 04 2011 *)
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CROSSREFS
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KEYWORD
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more,nonn
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AUTHOR
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EXTENSIONS
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a(22) was found in 2002 by Wilfrid Keller.
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STATUS
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approved
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