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%I M2234 N0886 #40 Jul 25 2023 19:47:13
%S 3,1,11,43,19,683,2731,331,43691,174763,5419,2796203,4051,87211,
%T 3033169,715827883,20857,86171,25781083,22366891,8831418697,
%U 2932031007403,18837001,165768537521,4363953127297,6529,28059810762433,48912491,160465489
%N Largest primitive factor of 2^(2n+1) + 1.
%C Also excludes intrinsic factors which is why a(1)=1 rather than 3. - _Sean A. Irvine_, Apr 20 2014
%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. 85.
%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="/A002589/b002589.txt">Table of n, a(n) for n = 0..560</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>
%K nonn
%O 0,1
%A _N. J. A. Sloane_
%E a(22)-a(472) from _Sean A. Irvine_, Apr 20 2014
%E a(473)-a(560) from _Max Alekseyev_, Feb 09 2020, Sep 10 2020, Dec 21 2022, Jul 25 2023
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