%I M2233 N0885 #24 Nov 24 2022 14:00:00
%S 3,1,11,43,19,683,2731,331,43691,174763,5419,2796203,251,87211,59,
%T 715827883,67,281,1777,22366891,83,2932031007403,18837001,283,
%U 4363953127297,307,107,2971,571,2833,768614336404564651,77158673929,131,7327657,139,56409643,1753
%N Smallest primitive factor of 2^(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. 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 Max Alekseyev, <a href="/A002185/b002185.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>
%Y Cf. A002589, A086257, A112927.
%K nonn
%O 0,1
%A _N. J. A. Sloane_
%E Terms a(25) onward from _Max Alekseyev_, Oct 16 2022