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A127581
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Smallest prime of the form k*2^n - 1, for k >= 2.
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17
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2, 3, 7, 23, 31, 127, 127, 383, 1279, 3583, 5119, 6143, 8191, 73727, 81919, 131071, 131071, 524287, 524287, 14680063, 14680063, 14680063, 109051903, 109051903, 654311423, 738197503, 738197503, 2147483647, 2147483647, 2147483647
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OFFSET
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0,1
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LINKS
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FORMULA
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EXAMPLE
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a(3)=23 because 23 = 3*2^3 - 1 is prime.
a(4)=31 because 31 = 2*2^4 - 1 is prime.
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MATHEMATICA
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a = {}; Do[k = 1; While[ !PrimeQ[k 2^n + 2^n - 1], k++ ]; AppendTo[a, k 2^n + 2^n - 1], {n, 0, 50}]; a
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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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