This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A242017 #19 May 24 2024 15:19:21 %S A242017 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 A242017 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 A242017 274177,3,5,3 %N A242017 Smallest prime factor of composites in the sequence A000051(n) = 2^n+1. %H A242017 Chai Wah Wu, <a href="/A242017/b242017.txt">Table of n, a(n) for n = 1..1786</a> %t A242017 FactorInteger[#][[1,1]]&/@Select[(2^Range[70]+1),CompositeQ] (* _Harvey P. Dale_, Feb 17 2017 *) %o A242017 (PARI) for(n=1, 1e2, if(!ispseudoprime(2^n+1), p=factor(2^n+1)[1, 1]; print1(p, ", "))) %Y A242017 Cf. A000051, A023394, A242016. %K A242017 nonn %O A242017 1,1 %A A242017 _Felix Fröhlich_, Aug 11 2014