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A005808 Numbers k such that (11^k - 1)/10 is prime.

%I A005808 M5032 #51 Apr 25 2025 05:18:27
%S A005808 17,19,73,139,907,1907,2029,4801,5153,10867,20161,293831,1868983
%N A005808 Numbers k such that (11^k - 1)/10 is prime.
%D A005808 J. Brillhart et al., Factorizations of b^n +- 1. Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 2nd edition, 1985; and later supplements.
%D A005808 Paulo Ribenboim, The Little Book of Bigger Primes, Springer-Verlag NY 2004. See p. 236.
%D A005808 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A005808 P. Bourdelais, <a href="https://listserv.nodak.edu/cgi-bin/wa.exe?A2=NMBRTHRY;417ab0d6.0906">A Generalized Repunit Conjecture</a>
%H A005808 J. Brillhart et al., <a href="http://dx.doi.org/10.1090/conm/022">Factorizations of b^n +- 1</a>, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
%H A005808 H. Dubner, <a href="http://dx.doi.org/10.1090/S0025-5718-1993-1185243-9">Generalized repunit primes</a>, Math. Comp., 61 (1993), 927-930.
%H A005808 H. Dubner, <a href="/A028491/a028491.pdf">Generalized repunit primes</a>, Math. Comp., 61 (1993), 927-930. [Annotated scanned copy]
%H A005808 H. Lifchitz, <a href="http://www.primenumbers.net/Henri/us/MersFermus.htm">Mersenne and Fermat primes field</a>
%H A005808 Henri & Renaud Lifchitz, <a href="http://www.primenumbers.net/prptop/searchform.php?form=%2811%5Ex-1%29%2F10&amp;action=Search">PRP Records</a>.
%H A005808 S. S. Wagstaff, Jr., <a href="http://www.cerias.purdue.edu/homes/ssw/cun/index.html">The Cunningham Project</a>
%H A005808 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Repunit.html">Repunit.</a>
%H A005808 <a href="/index/Pri#primepop">Index to primes in various ranges</a>, form ((k+1)^n-1)/k
%t A005808 lst={};Do[If[PrimeQ[(11^n-1)/10], Print[n];AppendTo[lst, n]], {n, 10^5}];lst (* _Vladimir Joseph Stephan Orlovsky_, Aug 21 2008 *)
%o A005808 (PARI) is(n)=ispseudoprime((11^n-1)/10) \\ _Charles R Greathouse IV_, Apr 29 2015
%K A005808 hard,more,nonn
%O A005808 1,1
%A A005808 _N. J. A. Sloane_
%E A005808 a(11) = 20161 was found by Kamil Duszenko on Aug 15 2003. - _Alexander Adamchuk_, Feb 11 2007
%E A005808 a(12) = 293831 corresponds to a probable prime discovered by _Paul Bourdelais_ with PFGW v3.3.1, Mar 08 2010
%E A005808 a(13) by _Paul Bourdelais_, Jun 01 2021