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A057173
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Numbers n such that (7^n + 1)/8 is a prime.
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1
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OFFSET
| 1,1
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COMMENTS
| (7^1619+1)/8, a 1368-digit number, has been certified prime with Primo. - Rick L. Shepherd (rshepherd2(AT)hotmail.com), May 19 2002
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LINKS
| J. Brillhart et al., Factorizations of b^n +- 1, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
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
H. Lifchitz, Mersenne and Fermat primes field
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MATHEMATICA
| lst={}; Do[p=(7^n+1)/8; If[PrimeQ[p], AppendTo[lst, n]], {n, 7!}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Sep 29 2008]
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PROG
| (Other) Using PFGW v3.3.1 [From Paul Bourdelais (pbourdelais(AT)radiantblue.com), Feb 17 2010]
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CROSSREFS
| Sequence in context: A019369 A019380 A126692 * A109371 A082372 A206626
Adjacent sequences: A057170 A057171 A057172 * A057174 A057175 A057176
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Sep 15 2000
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EXTENSIONS
| a(9)=106187 is a probable prime based on Fermat primality testing and trial factoring to 2E13. - Paul Bourdelais (paul.bourdelais(AT)gd-ais.com), Apr 07 2008
a(10)=201653 is a probable prime discovered by Paul Bourdelais (pbourdelais(AT)radiantblue.com), Feb 17 2010
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