%I A003020 M4790
%S A003020 11,37,101,271,37,4649,137,333667,9091,513239,9901,265371653,909091,
%T A003020 2906161,5882353,5363222357,333667,1111111111111111111,27961,10838689,
%U A003020 513239,11111111111111111111111,99990001,182521213001,1058313049
%N A003020 Largest prime factor of the "repunit" number 11...1 (cf. A002275)
%D A003020 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A003020 J. Brillhart et al., Factorizations of b^n +- 1. Contemporary Mathematics, 
               Vol. 22, Amer. Math. Soc., Providence, RI, 2nd edition, 1985; and 
               later supplements.
%D A003020 M. Kraitchik, Introduction \`{a} la Th\'{e}orie des Nombres. Gauthier-Villars, 
               Paris, 1952, p. 40.
%D A003020 David Wells, The Factors of the Repunits 11 through R_40, The Penguin 
               Dictionary of Curious and Interesting Numbers, p. 219 Penguin 1986.
%H A003020 T. D. Noe, <a href="b003020.txt">Table of n, a(n) for n=2..100</a> (derived 
               from Yousuke Koide)
%H A003020 J. Brillhart et al., <a href="http://www.ams.org/online_bks/conm22/">
               Factorizations of b^n +- 1</a>, Contemporary Mathematics, Vol. 22, 
               Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
%H A003020 P. de Geest, <a href="http://www.worldofnumbers.com/repunits.htm">Repunits 
               and their Prime Factors</a>
%H A003020 Makoto Kamada, <a href="http://homepage2.nifty.com/m_kamada/math/11111.htm">
               Factorizations of 11...11 (repunit)</a>.
%H A003020 Yousuke Koide, <a href="http://www.h4.dion.ne.jp/~rep/">Factorizations 
               of Repunit Numbers</a>
%H A003020 A. A. D. Steward, <a href="http://www.users.globalnet.co.uk/~aads/F010.txt">
               Factorization of Repunits[up to R(196)]</a> [Broken link]
%H A003020 S. S. Wagstaff, Jr., <a href="http://www.cerias.purdue.edu/homes/ssw/
               cun/index.html">The Cunningham Project</a>
%t A003020 Table[Max[Transpose[FactorInteger[10^i - 1]][[1]]], {i, 2, 25}]
%o A003020 (PARI) a(n)=local(p); if(n<2,n==1,p=factor((10^n-1)/9)~[1,]; p[length(p)])
%Y A003020 Cf. A002275, A102380. Same as A005422 except for initial terms. Smallest 
               factor: A067063.
%Y A003020 Sequence in context: A090950 A124479 A140373 this_sequence A075024 A152094 
               A147556
%Y A003020 Adjacent sequences: A003017 A003018 A003019 this_sequence A003021 A003022 
               A003023
%K A003020 nonn,nice
%O A003020 2,1
%A A003020 N. J. A. Sloane (njas(AT)research.att.com).
%E A003020 More terms from Harvey P. Dale (hpd1(AT)nyu.edu), Jan 17 2001