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A057173
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Numbers n such that (7^n + 1)/8 is a prime.
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14
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OFFSET
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1,1
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COMMENTS
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(7^1619+1)/8, a 1368-digit number, has been certified prime with Primo. - Rick L. Shepherd, May 19 2002
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LINKS
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J. Brillhart et al., Factorizations of b^n +- 1, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
Eric Weisstein's World of Mathematics, Repunit
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MATHEMATICA
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PROG
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(PARI) isok(n) = (denominator(p=(7^n+1)/8)==1) && isprime(p); \\ Michel Marcus, Oct 30 2017
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CROSSREFS
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KEYWORD
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nonn,changed
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AUTHOR
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EXTENSIONS
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a(9)=106187 is a probable prime based on Fermat primality testing and trial factoring to 2E13. - Paul Bourdelais, Apr 07 2008
a(10)=201653 is a probable prime discovered by Paul Bourdelais, Feb 17 2010
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STATUS
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proposed
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