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A242017 Smallest prime factor of composites in the sequence A000051(n) = 2^n+1. 2
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, 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, 274177, 3, 5, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Chai Wah Wu, Table of n, a(n) for n = 1..1786

MATHEMATICA

FactorInteger[#][[1, 1]]&/@Select[(2^Range[70]+1), CompositeQ] (* Harvey P. Dale, Feb 17 2017 *)

PROG

(PARI) for(n=1, 1e2, if(!ispseudoprime(2^n+1), p=factor(2^n+1)[1, 1]; print1(p, ", ")))

CROSSREFS

Cf. A023394, A242016.

Sequence in context: A138479 A202106 A136019 * A063714 A235649 A113965

Adjacent sequences:  A242014 A242015 A242016 * A242018 A242019 A242020

KEYWORD

nonn

AUTHOR

Felix Fröhlich, Aug 11 2014

STATUS

approved

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Last modified September 18 14:45 EDT 2020. Contains 337169 sequences. (Running on oeis4.)