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A003021 Largest factor of 10^n + 1.
(Formerly M2007)
7
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

Ray Chandler, Table of n, a(n) for n = 0..310 (first 281 terms from D. S. McNeil)

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

STATUS

approved

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Last modified December 13 15:03 EST 2018. Contains 318086 sequences. (Running on oeis4.)