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A263500
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Smallest positive b such that for all k >= 1 the numbers n*b^k + 1 are composite and gcd(n+1, b-1) = 1, or 0 if n > 1 is of the form 2^m - 1.
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0
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OFFSET
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3,2
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COMMENTS
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a(2) = 131072, or it is a Sierpiński number multiplied by a power of 2.
Because a(1) = 8 but a(2) is unknown, we do not include it here; we set the offset to 3.
a(2) <= 201446503145165177.
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LINKS
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CROSSREFS
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KEYWORD
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nonn,more,hard
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AUTHOR
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STATUS
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approved
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