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%I M4886 N2095 #47 Oct 19 2022 09:16:24
%S 2,13,11,1093,757,3851,797161,4561,34511,363889,368089,1001523179,
%T 391151,8209,20381027,4404047,2413941289,2664097031,17189128703,
%U 797161,86950696619,380808546861411923,927001,96656723,131713,99810171997
%N Largest prime factor of 3^(2n+1) - 1.
%D 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 M. Kraitchik, Recherches sur la Théorie des Nombres. Gauthiers-Villars, Paris, Vol. 1, 1924, Vol. 2, 1929, see Vol. 2, p. 28.
%D N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H <a href="/A002591/b002591.txt">Table of n, a(n) for n = 0..344</a>
%H 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 S. S. Wagstaff, Jr., <a href="http://www.cerias.purdue.edu/homes/ssw/cun/index.html">The Cunningham Project</a>
%F a(n) = A074477(2n+1). - _Max Alekseyev_, May 22 2022
%t Table[FactorInteger[3^(2n-1)-1][[-1,1]],{n,30}] (* _Harvey P. Dale_, Oct 19 2022 *)
%Y Together with A274909 forms bisection of A074477.Cf. A057958, A059885, A085028, A133801, A235366.
%K nonn
%O 0,1
%A _N. J. A. Sloane_
%E Corrected and extended by _Jud McCranie_, Jan 03 2001
%E Terms up to a(307) in b-file from _Sean A. Irvine_, Apr 20 2014
%E a(0) prepended and a(308)-a(344) added to b-file by _Max Alekseyev_, Apr 24 2019, Sep 10 2020, Aug 26 2021, May 22 2022
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