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A126659
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Least number k>0 such that ((2n-1)^k + 1)/(2n) is prime, or 0 if no such prime exists.
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1
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3, 5, 3, 3, 5, 3, 3, 7, 17, 3, 11, 3, 0, 7, 109, 5, 11, 5, 3, 17, 5, 103, 5, 7, 3, 21943, 3, 53, 17, 7, 3, 19, 3, 11, 5, 7, 5, 37, 3, 3, 19, 167, 7, 13, 3, 89, 43
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,1
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COMMENTS
| All terms are odd primes.
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LINKS
| H. Dubner and T. Granlund, Primes of the Form (b^n+1)/(b+1), J. Integer Sequences, 3 (2000), #P00.2.7.
Eric Weisstein's World of Mathematics, Repunit.
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FORMULA
| a(n) = A084742(2n-1).
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CROSSREFS
| Cf. A084741, A084742, A125954, A125958.
Sequence in context: A135514 A092553 A112755 * A102294 A021287 A124887
Adjacent sequences: A126656 A126657 A126658 * A126660 A126661 A126662
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KEYWORD
| hard,more,nonn
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AUTHOR
| Alexander Adamchuk (alex(AT)kolmogorov.com), Feb 09 2007, Feb 10 2007
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