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A005808
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Numbers k such that (11^k - 1)/10 is prime.
(Formerly M5032)
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18
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17, 19, 73, 139, 907, 1907, 2029, 4801, 5153, 10867, 20161, 293831, 1868983
(list;
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refs;
listen;
history;
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internal format)
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OFFSET
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1,1
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REFERENCES
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J. Brillhart et al., Factorizations of b^n +- 1. Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 2nd edition, 1985; and later supplements.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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Table of n, a(n) for n=1..13.
P. Bourdelais, A Generalized Repunit Conjecture
J. Brillhart et al., Factorizations of b^n +- 1, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
H. Dubner, Generalized repunit primes, Math. Comp., 61 (1993), 927-930.
H. Dubner, Generalized repunit primes, Math. Comp., 61 (1993), 927-930. [Annotated scanned copy]
H. Lifchitz, Mersenne and Fermat primes field
Henri & Renaud Lifchitz, PRP Records.
S. S. Wagstaff, Jr., The Cunningham Project
Eric Weisstein's World of Mathematics, Repunit.
Index to primes in various ranges, form ((k+1)^n-1)/k
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MATHEMATICA
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lst={}; Do[If[PrimeQ[(11^n-1)/10], Print[n]; AppendTo[lst, n]], {n, 10^5}]; lst (* Vladimir Joseph Stephan Orlovsky, Aug 21 2008 *)
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PROG
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(PARI) is(n)=ispseudoprime((11^n-1)/10) \\ Charles R Greathouse IV, Apr 29 2015
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CROSSREFS
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Sequence in context: A232882 A232878 A226681 * A180559 A272478 A028489
Adjacent sequences: A005805 A005806 A005807 * A005809 A005810 A005811
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KEYWORD
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hard,nonn
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AUTHOR
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N. J. A. Sloane
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EXTENSIONS
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a(11) = 20161 was found by Kamil Duszenko on Aug 15 2003. - Alexander Adamchuk, Feb 11 2007
a(12) = 293831 corresponds to a probable prime discovered by Paul Bourdelais with PFGW v3.3.1, Mar 08 2010
a(13) by Paul Bourdelais, Jun 01 2021
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STATUS
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approved
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