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A242017
Smallest prime factor of composites in the sequence A000051(n) = 2^n+1.
3
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
OFFSET
1,1
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
KEYWORD
nonn
AUTHOR
Felix Fröhlich, Aug 11 2014
STATUS
approved