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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
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.
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
Sequence in context: A001271 A038371 A236174 * A097463 A263607 A083394
KEYWORD
nonn,easy
AUTHOR
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.)