%I #19 May 24 2024 15:19:21
%S 3,3,5,3,3,5,3,17,3,5,3,3,5,3,17,3,5,3,97,3,5,3,17,3,5,3,641,3,5,3,17,
%T 3,5,3,257,3,5,3,17,3,5,3,193,3,5,3,17,3,5,3,257,3,5,3,17,3,5,3,
%U 274177,3,5,3
%N Smallest prime factor of composites in the sequence A000051(n) = 2^n+1.
%H Chai Wah Wu, <a href="/A242017/b242017.txt">Table of n, a(n) for n = 1..1786</a>
%t FactorInteger[#][[1,1]]&/@Select[(2^Range[70]+1),CompositeQ] (* _Harvey P. Dale_, Feb 17 2017 *)
%o (PARI) for(n=1, 1e2, if(!ispseudoprime(2^n+1), p=factor(2^n+1)[1, 1]; print1(p, ", ")))
%Y Cf. A000051, A023394, A242016.
%K nonn
%O 1,1
%A _Felix Fröhlich_, Aug 11 2014
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