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A003020 Largest prime factor of the "repunit" number 11...1 (cf. A002275).
(Formerly M4790)
21
11, 37, 101, 271, 37, 4649, 137, 333667, 9091, 513239, 9901, 265371653, 909091, 2906161, 5882353, 5363222357, 333667, 1111111111111111111, 27961, 10838689, 513239, 11111111111111111111111, 99990001, 182521213001, 1058313049 (list; graph; refs; listen; history; text; internal format)
OFFSET
2,1
COMMENTS
a(n) = R_n iff n is a term of A004023. - Bernard Schott, Jul 07 2022
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.
M. Kraitchik, Introduction à la Théorie des Nombres. Gauthier-Villars, Paris, 1952, p. 40.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
David Wells, The Factors of the Repunits 11 through R_40, The Penguin Dictionary of Curious and Interesting Numbers, Penguin Books, 1986, p. 219.
LINKS
Max Alekseyev, Table of n, a(n) for n = 2..352 (terms a(2)..a(100) from T. D. Noe, derived from data from Yousuke Koide; a(101)..a(322) from Ray Chandler)
J. Brillhart et al., Factorizations of b^n +- 1, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
A. A. D. Steward, Factorization of Repunits[up to R(196)] [Broken link]
S. S. Wagstaff, Jr., The Cunningham Project
FORMULA
a(n) = A006530(A002275(n)). - Ray Chandler, Apr 22 2017
MATHEMATICA
Table[Max[Transpose[FactorInteger[10^i - 1]][[1]]], {i, 2, 25}]
Table[FactorInteger[FromDigits[PadRight[{}, n, 1]]][[-1, 1]], {n, 2, 30}] (* Harvey P. Dale, Feb 01 2014 *)
PROG
(PARI) a(n)=local(p); if(n<2, n==1, p=factor((10^n-1)/9)~[1, ]; p[length(p)])
CROSSREFS
Same as A005422 except for initial terms.
Smallest factor: A067063.
Sequence in context: A124479 A140373 A316191 * A075024 A229612 A297797
KEYWORD
nonn,nice
AUTHOR
EXTENSIONS
More terms from Harvey P. Dale, Jan 17 2001
STATUS
approved

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Last modified May 18 08:25 EDT 2024. Contains 372618 sequences. (Running on oeis4.)