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A003021
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Largest prime factor of 10^n + 1.
(Formerly M2007)
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9
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2, 11, 101, 13, 137, 9091, 9901, 909091, 5882353, 52579, 27961, 8779, 99990001, 1058313049, 121499449, 9091, 69857, 21993833369, 999999000001, 909090909090909091, 5964848081, 909091, 1056689261, 549797184491917
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OFFSET
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0,1
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REFERENCES
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J. Brillhart et al., Factorizations of b^n +- 1. Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 2nd edition, 1985; and later supplements.
Ehrhard Behrends, Five-Minute Mathematics, translated by David Kramer. American Mathematical Society (2008) p. 7
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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Table of n, a(n) for n = 0..322
J. Brillhart et al., Factorizations of b^n +- 1, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
T. Granlund, Factors of 10^n + 1
Makoto Kamada, Factorizations of 100...001.
S. S. Wagstaff, Jr., The Cunningham Project
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FORMULA
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a(n) = A006530(A062397(n)). - Vincenzo Librandi, Jul 12 2016
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MATHEMATICA
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Table[FactorInteger[10^n + 1][[-1, 1]], {n, 0, 29}] (* Alonso del Arte, Oct 21 2011 *)
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PROG
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(PARI) for(n=0, 1e2, p=factor(10^n+1)[omega(10^n+1), 1]; print1(p, ", ")) \\ Felix Fröhlich, Aug 13 2014
(MAGMA) [Maximum(PrimeDivisors(10^n+1)): n in [0..40]]; // Vincenzo Librandi, Jul 12 2016
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CROSSREFS
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Cf. A006530, A062397.
Sequence in context: A001271 A038371 A236174 * A097463 A263607 A083394
Adjacent sequences: A003018 A003019 A003020 * A003022 A003023 A003024
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KEYWORD
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nonn,easy
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AUTHOR
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N. J. A. Sloane.
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EXTENSIONS
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More terms from Jason Earls, Jul 11 2001
Terms up to a(280) in b-file from D. S. McNeil, Oct 22 2011
a(281)-a(310) in b-file from Ray Chandler, May 02 2017
a(311)-a(322) in b-file from Max Alekseyev, Apr 24 2019, Feb 13 2020
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STATUS
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approved
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