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 A003021 Largest prime factor of 10^n + 1. (Formerly M2007) 13
 2, 11, 101, 13, 137, 9091, 9901, 909091, 5882353, 52579, 27961, 8779, 99990001, 1058313049, 121499449, 9091, 69857, 21993833369, 999999000001, 909090909090909091, 5964848081, 909091, 1056689261, 549797184491917 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 REFERENCES 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). LINKS Table of n, a(n) for n = 0..331 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. FORMULA a(n) = A006530(A062397(n)). - Vincenzo Librandi, Jul 12 2016 MATHEMATICA Table[FactorInteger[10^n + 1][[-1, 1]], {n, 0, 29}] (* Alonso del Arte, Oct 21 2011 *) PROG (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 CROSSREFS Cf. A006530, A062397. Sequence in context: A001271 A038371 A236174 * A097463 A263607 A083394 Adjacent sequences: A003018 A003019 A003020 * A003022 A003023 A003024 KEYWORD nonn,easy AUTHOR N. J. A. Sloane EXTENSIONS 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(331) in b-file from Max Alekseyev, Apr 24 2019, Feb 13 2020, May 13 2022 STATUS approved

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Last modified April 23 18:16 EDT 2024. Contains 371916 sequences. (Running on oeis4.)