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A242017 Smallest prime factor of composites in the sequence A000051(n) = 2^n+1. 2

%I #17 Oct 10 2019 04:01:51

%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. A023394, A242016.

%K nonn

%O 1,1

%A _Felix Fröhlich_, Aug 11 2014

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Last modified March 28 22:04 EDT 2024. Contains 371254 sequences. (Running on oeis4.)